diff --git a/CHANGELOG.md b/CHANGELOG.md
index ae6d311560..765f483145 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,6 @@
 ## main / (unreleased)
 
-* [CHANGE] ...
+* [CHANGE] slack: Derive the `chat.update` URL from the configured `api_url` base instead of using the hardcoded `https://slack.com/api/chat.update`. Standard configurations are unaffected; deployments that point `api_url` at a Slack-compatible proxy/forwarder will now have their update requests routed to that same host. #5225
 * [FEATURE] ...
 * [ENHANCEMENT] ...
 
diff --git a/config/config.go b/config/config.go
index 0d6899122c..0b96b2c586 100644
--- a/config/config.go
+++ b/config/config.go
@@ -36,6 +36,7 @@ import (
 	"github.com/prometheus/alertmanager/notify/incidentio"
 	"github.com/prometheus/alertmanager/notify/jira"
 	"github.com/prometheus/alertmanager/notify/mattermost"
+	"github.com/prometheus/alertmanager/notify/slack"
 	"github.com/prometheus/alertmanager/notify/webhook"
 	"github.com/prometheus/alertmanager/timeinterval"
 	"github.com/prometheus/alertmanager/tracing"
@@ -411,7 +412,7 @@ func (c *Config) UnmarshalYAML(unmarshal func(any) error) error {
 		}
 		for _, sc := range rcv.SlackConfigs {
 			if sc == nil {
-				sc = &SlackConfig{}
+				sc = &slack.SlackConfig{}
 			}
 			sc.AppURL = cmp.Or(sc.AppURL, c.Global.SlackAppURL)
 			if sc.AppURL == nil {
@@ -429,6 +430,9 @@ func (c *Config) UnmarshalYAML(unmarshal func(any) error) error {
 			if sc.APIURL == nil && len(sc.APIURLFile) == 0 && sc.AppToken == "" && len(sc.AppTokenFile) == 0 {
 				return errors.New("no Slack API URL nor App token set either inline or in a file")
 			}
+			if err := sc.ValidateMessageStrategy(); err != nil {
+				return err
+			}
 			if sc.HTTPConfig == nil {
 				// we don't want to change the global http config when setting the receiver's http config, do we do a copy
 				httpconfig := *c.Global.HTTPConfig
@@ -947,7 +951,7 @@ type Receiver struct {
 	EmailConfigs      []*EmailConfig                 `yaml:"email_configs,omitempty" json:"email_configs,omitempty"`
 	IncidentioConfigs []*incidentio.IncidentioConfig `yaml:"incidentio_configs,omitempty" json:"incidentio_configs,omitempty"`
 	PagerdutyConfigs  []*PagerdutyConfig             `yaml:"pagerduty_configs,omitempty" json:"pagerduty_configs,omitempty"`
-	SlackConfigs      []*SlackConfig                 `yaml:"slack_configs,omitempty" json:"slack_configs,omitempty"`
+	SlackConfigs      []*slack.SlackConfig           `yaml:"slack_configs,omitempty" json:"slack_configs,omitempty"`
 	WebhookConfigs    []*webhook.WebhookConfig       `yaml:"webhook_configs,omitempty" json:"webhook_configs,omitempty"`
 	OpsGenieConfigs   []*OpsGenieConfig              `yaml:"opsgenie_configs,omitempty" json:"opsgenie_configs,omitempty"`
 	WechatConfigs     []*WechatConfig                `yaml:"wechat_configs,omitempty" json:"wechat_configs,omitempty"`
diff --git a/config/config_test.go b/config/config_test.go
index 9f920dd39e..29de1df689 100644
--- a/config/config_test.go
+++ b/config/config_test.go
@@ -1072,13 +1072,106 @@ func TestSlackBothAppTokenAndAPIURL(t *testing.T) {
 	}
 }
 
-func TestSlackUpdateMessageWebhookURL(t *testing.T) {
-	_, err := LoadFile("testdata/conf.slack-update-message-and-webhook.yml")
+func TestSlackMessageStrategyWithWrongAPIURL(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name     string
+		file     string
+		strategy string
+	}{
+		{
+			name:     "update strategy with webhook URL",
+			file:     "testdata/conf.slack-update-message-and-webhook.yml",
+			strategy: `update`,
+		},
+		{
+			name:     "update strategy with webhook URL (new field)",
+			file:     "testdata/conf.slack-update-message-and-webhook-with-new-field.yml",
+			strategy: `update`,
+		},
+		{
+			name:     "thread strategy with webhook URL",
+			file:     "testdata/conf.slack-thread-message-and-webhook.yml",
+			strategy: `thread`,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			_, err := LoadFile(tt.file)
+			if err == nil {
+				t.Fatal("Expected an error")
+			}
+			expectedErrMsg := fmt.Sprintf("message_strategy %q requires a bot token; api_url must be https://slack.com/api/chat.postMessage", tt.strategy)
+			if err.Error() != expectedErrMsg {
+				t.Errorf("Expected: %s\nGot: %s", expectedErrMsg, err.Error())
+			}
+		})
+	}
+}
+
+func TestSlackMessageStrategyWithGlobalAPIURL(t *testing.T) {
+	t.Parallel()
+
+	_, err := LoadFile("testdata/conf.slack-thread-strategy-with-global-api-url.yml")
+	if err != nil {
+		t.Fatalf("Expected no error when message_strategy uses global slack_api_url, got: %s", err)
+	}
+}
+
+func TestSlackMessageStrategyWithoutAPIURL(t *testing.T) {
+	t.Parallel()
+
+	_, err := LoadFile("testdata/conf.slack-thread-strategy-without-api-url.yml")
 	if err == nil {
-		t.Fatalf("Expected an error parsing %s: %s", "testdata/conf.slack-update-message-and-webhook", err)
+		t.Fatal("Expected an error when message_strategy: thread has no api_url at any level")
+	}
+	expectedErrMsg := `no Slack API URL nor App token set either inline or in a file`
+	if err.Error() != expectedErrMsg {
+		t.Errorf("Expected: %s\nGot: %s", expectedErrMsg, err.Error())
+	}
+}
+
+func TestSlackThreadedOptionsValidation(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name           string
+		file           string
+		expectedErrMsg string
+	}{
+		{
+			name:           "threaded options without thread strategy (resolve emoji)",
+			file:           "testdata/conf.slack-thread-resolve-emoji-without-thread-message.yml",
+			expectedErrMsg: `threaded_options requires message_strategy to be "thread"`,
+		},
+		{
+			name:           "threaded options without thread strategy (update parent)",
+			file:           "testdata/conf.slack-thread-update-parent-without-thread-message.yml",
+			expectedErrMsg: `threaded_options requires message_strategy to be "thread"`,
+		},
+		{
+			name:           "resolve color without summary header",
+			file:           "testdata/conf.slack-resolve-color-without-summary-header.yml",
+			expectedErrMsg: `threaded_options.summary_header requires use_summary_header to be enabled`,
+		},
 	}
-	if err.Error() != "update_message can only be used with bot tokens. api_url must be set to https://slack.com/api/chat.postMessage" {
-		t.Errorf("Expected: %s\nGot: %s", "update_message can only be used with bot tokens. api_url must be set to https://slack.com/api/chat.postMessage", err.Error())
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			_, err := LoadFile(tt.file)
+			if err == nil {
+				t.Fatal("Expected an error")
+			}
+			if err.Error() != tt.expectedErrMsg {
+				t.Errorf("Expected: %s\nGot: %s", tt.expectedErrMsg, err.Error())
+			}
+		})
 	}
 }
 
diff --git a/config/notifiers.go b/config/notifiers.go
index c58698fbee..7ab80a82c6 100644
--- a/config/notifiers.go
+++ b/config/notifiers.go
@@ -69,23 +69,6 @@ var (
 		ClientURL:   `{{ template "pagerduty.default.clientURL" . }}`,
 	}
 
-	// DefaultSlackConfig defines default values for Slack configurations.
-	DefaultSlackConfig = SlackConfig{
-		NotifierConfig: amcommoncfg.NotifierConfig{
-			VSendResolved: false,
-		},
-		Color:      `{{ template "slack.default.color" . }}`,
-		Username:   `{{ template "slack.default.username" . }}`,
-		Title:      `{{ template "slack.default.title" . }}`,
-		TitleLink:  `{{ template "slack.default.titlelink" . }}`,
-		IconEmoji:  `{{ template "slack.default.iconemoji" . }}`,
-		IconURL:    `{{ template "slack.default.iconurl" . }}`,
-		Pretext:    `{{ template "slack.default.pretext" . }}`,
-		Text:       `{{ template "slack.default.text" . }}`,
-		Fallback:   `{{ template "slack.default.fallback" . }}`,
-		CallbackID: `{{ template "slack.default.callbackid" . }}`,
-		Footer:     `{{ template "slack.default.footer" . }}`,
-	}
 	// DefaultRocketchatConfig defines default values for Rocketchat configurations.
 	DefaultRocketchatConfig = RocketchatConfig{
 		NotifierConfig: amcommoncfg.NotifierConfig{
@@ -352,160 +335,6 @@ func (c *PagerdutyConfig) UnmarshalYAML(unmarshal func(any) error) error {
 	return nil
 }
 
-// SlackAction configures a single Slack action that is sent with each notification.
-// See https://api.slack.com/docs/message-attachments#action_fields and https://api.slack.com/docs/message-buttons
-// for more information.
-type SlackAction struct {
-	Type         string                  `yaml:"type,omitempty"  json:"type,omitempty"`
-	Text         string                  `yaml:"text,omitempty"  json:"text,omitempty"`
-	URL          string                  `yaml:"url,omitempty"   json:"url,omitempty"`
-	Style        string                  `yaml:"style,omitempty" json:"style,omitempty"`
-	Name         string                  `yaml:"name,omitempty"  json:"name,omitempty"`
-	Value        string                  `yaml:"value,omitempty"  json:"value,omitempty"`
-	ConfirmField *SlackConfirmationField `yaml:"confirm,omitempty"  json:"confirm,omitempty"`
-}
-
-// UnmarshalYAML implements the yaml.Unmarshaler interface for SlackAction.
-func (c *SlackAction) UnmarshalYAML(unmarshal func(any) error) error {
-	type plain SlackAction
-	if err := unmarshal((*plain)(c)); err != nil {
-		return err
-	}
-	if c.Type == "" {
-		return errors.New("missing type in Slack action configuration")
-	}
-	if c.Text == "" {
-		return errors.New("missing text in Slack action configuration")
-	}
-	if c.URL != "" {
-		// Clear all message action fields.
-		c.Name = ""
-		c.Value = ""
-		c.ConfirmField = nil
-	} else if c.Name != "" {
-		c.URL = ""
-	} else {
-		return errors.New("missing name or url in Slack action configuration")
-	}
-	return nil
-}
-
-// SlackConfirmationField protect users from destructive actions or particularly distinguished decisions
-// by asking them to confirm their button click one more time.
-// See https://api.slack.com/docs/interactive-message-field-guide#confirmation_fields for more information.
-type SlackConfirmationField struct {
-	Text        string `yaml:"text,omitempty"  json:"text,omitempty"`
-	Title       string `yaml:"title,omitempty"  json:"title,omitempty"`
-	OkText      string `yaml:"ok_text,omitempty"  json:"ok_text,omitempty"`
-	DismissText string `yaml:"dismiss_text,omitempty"  json:"dismiss_text,omitempty"`
-}
-
-// UnmarshalYAML implements the yaml.Unmarshaler interface for SlackConfirmationField.
-func (c *SlackConfirmationField) UnmarshalYAML(unmarshal func(any) error) error {
-	type plain SlackConfirmationField
-	if err := unmarshal((*plain)(c)); err != nil {
-		return err
-	}
-	if c.Text == "" {
-		return errors.New("missing text in Slack confirmation configuration")
-	}
-	return nil
-}
-
-// SlackField configures a single Slack field that is sent with each notification.
-// Each field must contain a title, value, and optionally, a boolean value to indicate if the field
-// is short enough to be displayed next to other fields designated as short.
-// See https://api.slack.com/docs/message-attachments#fields for more information.
-type SlackField struct {
-	Title string `yaml:"title,omitempty" json:"title,omitempty"`
-	Value string `yaml:"value,omitempty" json:"value,omitempty"`
-	Short *bool  `yaml:"short,omitempty" json:"short,omitempty"`
-}
-
-// UnmarshalYAML implements the yaml.Unmarshaler interface for SlackField.
-func (c *SlackField) UnmarshalYAML(unmarshal func(any) error) error {
-	type plain SlackField
-	if err := unmarshal((*plain)(c)); err != nil {
-		return err
-	}
-	if c.Title == "" {
-		return errors.New("missing title in Slack field configuration")
-	}
-	if c.Value == "" {
-		return errors.New("missing value in Slack field configuration")
-	}
-	return nil
-}
-
-// SlackConfig configures notifications via Slack.
-type SlackConfig struct {
-	amcommoncfg.NotifierConfig `yaml:",inline" json:",inline"`
-
-	HTTPConfig *commoncfg.HTTPClientConfig `yaml:"http_config,omitempty" json:"http_config,omitempty"`
-
-	APIURL       *amcommoncfg.SecretURL `yaml:"api_url,omitempty" json:"api_url,omitempty"`
-	APIURLFile   string                 `yaml:"api_url_file,omitempty" json:"api_url_file,omitempty"`
-	AppToken     commoncfg.Secret       `yaml:"app_token,omitempty" json:"app_token,omitempty"`
-	AppTokenFile string                 `yaml:"app_token_file,omitempty" json:"app_token_file,omitempty"`
-	AppURL       *amcommoncfg.URL       `yaml:"app_url,omitempty" json:"app_url,omitempty"`
-
-	// Slack channel override, (like #other-channel or @username).
-	Channel  string `yaml:"channel,omitempty" json:"channel,omitempty"`
-	Username string `yaml:"username,omitempty" json:"username,omitempty"`
-	Color    string `yaml:"color,omitempty" json:"color,omitempty"`
-
-	Title       string         `yaml:"title,omitempty" json:"title,omitempty"`
-	TitleLink   string         `yaml:"title_link,omitempty" json:"title_link,omitempty"`
-	Pretext     string         `yaml:"pretext,omitempty" json:"pretext,omitempty"`
-	Text        string         `yaml:"text,omitempty" json:"text,omitempty"`
-	MessageText string         `yaml:"message_text,omitempty" json:"message_text,omitempty"`
-	Fields      []*SlackField  `yaml:"fields,omitempty" json:"fields,omitempty"`
-	ShortFields bool           `yaml:"short_fields" json:"short_fields,omitempty"`
-	Footer      string         `yaml:"footer,omitempty" json:"footer,omitempty"`
-	Fallback    string         `yaml:"fallback,omitempty" json:"fallback,omitempty"`
-	CallbackID  string         `yaml:"callback_id,omitempty" json:"callback_id,omitempty"`
-	IconEmoji   string         `yaml:"icon_emoji,omitempty" json:"icon_emoji,omitempty"`
-	IconURL     string         `yaml:"icon_url,omitempty" json:"icon_url,omitempty"`
-	ImageURL    string         `yaml:"image_url,omitempty" json:"image_url,omitempty"`
-	ThumbURL    string         `yaml:"thumb_url,omitempty" json:"thumb_url,omitempty"`
-	LinkNames   bool           `yaml:"link_names" json:"link_names,omitempty"`
-	MrkdwnIn    []string       `yaml:"mrkdwn_in,omitempty" json:"mrkdwn_in,omitempty"`
-	Actions     []*SlackAction `yaml:"actions,omitempty" json:"actions,omitempty"`
-
-	// UpdateMessage enables updating existing Slack messages instead of creating new ones.
-	// Requires bot token with chat:write scope. Webhook URLs do not support updates.
-
-	UpdateMessage bool `yaml:"update_message" json:"update_message,omitempty"`
-	// Timeout is the maximum time allowed to invoke the slack. Setting this to 0
-	// does not impose a timeout.
-	Timeout time.Duration `yaml:"timeout" json:"timeout"`
-}
-
-// UnmarshalYAML implements the yaml.Unmarshaler interface.
-func (c *SlackConfig) UnmarshalYAML(unmarshal func(any) error) error {
-	*c = DefaultSlackConfig
-	type plain SlackConfig
-	if err := unmarshal((*plain)(c)); err != nil {
-		return err
-	}
-
-	if c.APIURL != nil && len(c.APIURLFile) > 0 {
-		return errors.New("at most one of api_url & api_url_file must be configured")
-	}
-	if c.AppToken != "" && len(c.AppTokenFile) > 0 {
-		return errors.New("at most one of app_token & app_token_file must be configured")
-	}
-	if (c.APIURL != nil || len(c.APIURLFile) > 0) && (c.AppToken != "" || len(c.AppTokenFile) > 0) {
-		return errors.New("at most one of api_url/api_url_file & app_token/app_token_file must be configured")
-	}
-
-	if c.UpdateMessage && c.APIURL.String() != "https://slack.com/api/chat.postMessage" {
-		return errors.New("update_message can only be used with bot tokens. api_url must be set to https://slack.com/api/chat.postMessage")
-	}
-
-	return nil
-}
-
 // WechatConfig configures notifications via Wechat.
 type WechatConfig struct {
 	amcommoncfg.NotifierConfig `yaml:",inline" json:",inline"`
diff --git a/config/notifiers_test.go b/config/notifiers_test.go
index 9b75b2ec99..31a303ea07 100644
--- a/config/notifiers_test.go
+++ b/config/notifiers_test.go
@@ -448,319 +448,6 @@ monospace: true
 	}
 }
 
-func TestLoadSlackConfiguration(t *testing.T) {
-	tests := []struct {
-		in       string
-		expected SlackConfig
-	}{
-		{
-			in: `
-color: green
-username: mark
-channel: engineering
-title_link: http://example.com/
-image_url: https://example.com/logo.png
-`,
-			expected: SlackConfig{
-				Color: "green", Username: "mark", Channel: "engineering",
-				TitleLink: "http://example.com/",
-				ImageURL:  "https://example.com/logo.png",
-			},
-		},
-		{
-			in: `
-color: green
-username: mark
-channel: alerts
-title_link: http://example.com/alert1
-mrkdwn_in:
-- pretext
-- text
-`,
-			expected: SlackConfig{
-				Color: "green", Username: "mark", Channel: "alerts",
-				MrkdwnIn: []string{"pretext", "text"}, TitleLink: "http://example.com/alert1",
-			},
-		},
-	}
-	for _, rt := range tests {
-		var cfg SlackConfig
-		err := yaml.UnmarshalStrict([]byte(rt.in), &cfg)
-		if err != nil {
-			t.Fatalf("\nerror returned when none expected, error:\n%v", err)
-		}
-		if rt.expected.Color != cfg.Color {
-			t.Errorf("\nexpected:\n%v\ngot:\n%v", rt.expected.Color, cfg.Color)
-		}
-		if rt.expected.Username != cfg.Username {
-			t.Errorf("\nexpected:\n%v\ngot:\n%v", rt.expected.Username, cfg.Username)
-		}
-		if rt.expected.Channel != cfg.Channel {
-			t.Errorf("\nexpected:\n%v\ngot:\n%v", rt.expected.Channel, cfg.Channel)
-		}
-		if rt.expected.ThumbURL != cfg.ThumbURL {
-			t.Errorf("\nexpected:\n%v\ngot:\n%v", rt.expected.ThumbURL, cfg.ThumbURL)
-		}
-		if rt.expected.TitleLink != cfg.TitleLink {
-			t.Errorf("\nexpected:\n%v\ngot:\n%v", rt.expected.TitleLink, cfg.TitleLink)
-		}
-		if rt.expected.ImageURL != cfg.ImageURL {
-			t.Errorf("\nexpected:\n%v\ngot:\n%v", rt.expected.ImageURL, cfg.ImageURL)
-		}
-		if len(rt.expected.MrkdwnIn) != len(cfg.MrkdwnIn) {
-			t.Errorf("\nexpected:\n%v\ngot:\n%v", rt.expected.MrkdwnIn, cfg.MrkdwnIn)
-		}
-		for i := range cfg.MrkdwnIn {
-			if rt.expected.MrkdwnIn[i] != cfg.MrkdwnIn[i] {
-				t.Errorf("\nexpected:\n%v\ngot:\n%v\nat index %v", rt.expected.MrkdwnIn[i], cfg.MrkdwnIn[i], i)
-			}
-		}
-	}
-}
-
-func TestSlackAuthMethodConfigValidation(t *testing.T) {
-	tests := []struct {
-		in          string
-		expectedErr string
-	}{
-		{
-			in: `
-api_url: 'https://hooks.slack.com/services/T00000000/B00000000/XXXXXXXXXXXXXXXXXXXXXXXX'
-api_url_file: /slack_url
-`,
-			expectedErr: "at most one of api_url & api_url_file must be configured",
-		},
-		{
-			in: `
-app_token: 'xoxb-1234-abcdefgh'
-app_token_file: /slack_app_token
-`,
-			expectedErr: "at most one of app_token & app_token_file must be configured",
-		},
-		{
-			in: `
-app_token: 'xoxb-1234-abcdefgh'
-api_url: 'https://hooks.slack.com/services/T00000000/B00000000/XXXXXXXXXXXXXXXXXXXXXXXX'
-`,
-			expectedErr: "at most one of api_url/api_url_file & app_token/app_token_file must be configured",
-		},
-	}
-
-	for _, rt := range tests {
-		var cfg SlackConfig
-		err := yaml.UnmarshalStrict([]byte(rt.in), &cfg)
-
-		// Check if an error occurred when it was NOT expected to.
-		if rt.expectedErr == "" && err != nil {
-			t.Fatalf("\nerror returned when none expected, error:\n%v", err)
-		}
-		// Check that an error occurred if one was expected to.
-		if rt.expectedErr != "" && err == nil {
-			t.Fatalf("\nno error returned, expected:\n%v", rt.expectedErr)
-		}
-		// Check that the error that occurred was what was expected.
-		if err != nil && err.Error() != rt.expectedErr {
-			t.Errorf("\nexpected:\n%v\ngot:\n%v", rt.expectedErr, err.Error())
-		}
-	}
-}
-
-func TestSlackFieldConfigValidation(t *testing.T) {
-	tests := []struct {
-		in       string
-		expected string
-	}{
-		{
-			in: `
-fields:
-- title: first
-  value: hello
-- title: second
-`,
-			expected: "missing value in Slack field configuration",
-		},
-		{
-			in: `
-fields:
-- title: first
-  value: hello
-  short: true
-- value: world
-  short: true
-`,
-			expected: "missing title in Slack field configuration",
-		},
-		{
-			in: `
-fields:
-- title: first
-  value: hello
-  short: true
-- title: second
-  value: world
-`,
-			expected: "",
-		},
-	}
-
-	for _, rt := range tests {
-		var cfg SlackConfig
-		err := yaml.UnmarshalStrict([]byte(rt.in), &cfg)
-
-		// Check if an error occurred when it was NOT expected to.
-		if rt.expected == "" && err != nil {
-			t.Fatalf("\nerror returned when none expected, error:\n%v", err)
-		}
-		// Check that an error occurred if one was expected to.
-		if rt.expected != "" && err == nil {
-			t.Fatalf("\nno error returned, expected:\n%v", rt.expected)
-		}
-		// Check that the error that occurred was what was expected.
-		if err != nil && err.Error() != rt.expected {
-			t.Errorf("\nexpected:\n%v\ngot:\n%v", rt.expected, err.Error())
-		}
-	}
-}
-
-func TestSlackFieldConfigUnmarshaling(t *testing.T) {
-	in := `
-fields:
-- title: first
-  value: hello
-  short: true
-- title: second
-  value: world
-- title: third
-  value: slack field test
-  short: false
-`
-	expected := []*SlackField{
-		{
-			Title: "first",
-			Value: "hello",
-			Short: newBoolPointer(true),
-		},
-		{
-			Title: "second",
-			Value: "world",
-			Short: nil,
-		},
-		{
-			Title: "third",
-			Value: "slack field test",
-			Short: newBoolPointer(false),
-		},
-	}
-
-	var cfg SlackConfig
-	err := yaml.UnmarshalStrict([]byte(in), &cfg)
-	if err != nil {
-		t.Fatalf("\nerror returned when none expected, error:\n%v", err)
-	}
-
-	for index, field := range cfg.Fields {
-		exp := expected[index]
-		if field.Title != exp.Title {
-			t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.Title, field.Title)
-		}
-		if field.Value != exp.Value {
-			t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.Value, field.Value)
-		}
-		if exp.Short == nil && field.Short != nil {
-			t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.Short, *field.Short)
-		}
-		if exp.Short != nil && field.Short == nil {
-			t.Errorf("\nexpected:\n%v\ngot:\n%v", *exp.Short, field.Short)
-		}
-		if exp.Short != nil && *exp.Short != *field.Short {
-			t.Errorf("\nexpected:\n%v\ngot:\n%v", *exp.Short, *field.Short)
-		}
-	}
-}
-
-func TestSlackActionsValidation(t *testing.T) {
-	in := `
-actions:
-- type: button
-  text: hello
-  url: https://localhost
-  style: danger
-- type: button
-  text: hello
-  name: something
-  style: default
-  confirm:
-    title: please confirm
-    text: are you sure?
-    ok_text: yes
-    dismiss_text: no
-`
-	expected := []*SlackAction{
-		{
-			Type:  "button",
-			Text:  "hello",
-			URL:   "https://localhost",
-			Style: "danger",
-		},
-		{
-			Type:  "button",
-			Text:  "hello",
-			Name:  "something",
-			Style: "default",
-			ConfirmField: &SlackConfirmationField{
-				Title:       "please confirm",
-				Text:        "are you sure?",
-				OkText:      "yes",
-				DismissText: "no",
-			},
-		},
-	}
-
-	var cfg SlackConfig
-	err := yaml.UnmarshalStrict([]byte(in), &cfg)
-	if err != nil {
-		t.Fatalf("\nerror returned when none expected, error:\n%v", err)
-	}
-
-	for index, action := range cfg.Actions {
-		exp := expected[index]
-		if action.Type != exp.Type {
-			t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.Type, action.Type)
-		}
-		if action.Text != exp.Text {
-			t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.Text, action.Text)
-		}
-		if action.URL != exp.URL {
-			t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.URL, action.URL)
-		}
-		if action.Style != exp.Style {
-			t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.Style, action.Style)
-		}
-		if action.Name != exp.Name {
-			t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.Name, action.Name)
-		}
-		if action.Value != exp.Value {
-			t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.Value, action.Value)
-		}
-		if action.ConfirmField != nil && exp.ConfirmField == nil || action.ConfirmField == nil && exp.ConfirmField != nil {
-			t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.ConfirmField, action.ConfirmField)
-		} else if action.ConfirmField != nil && exp.ConfirmField != nil {
-			if action.ConfirmField.Title != exp.ConfirmField.Title {
-				t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.ConfirmField.Title, action.ConfirmField.Title)
-			}
-			if action.ConfirmField.Text != exp.ConfirmField.Text {
-				t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.ConfirmField.Text, action.ConfirmField.Text)
-			}
-			if action.ConfirmField.OkText != exp.ConfirmField.OkText {
-				t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.ConfirmField.OkText, action.ConfirmField.OkText)
-			}
-			if action.ConfirmField.DismissText != exp.ConfirmField.DismissText {
-				t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.ConfirmField.DismissText, action.ConfirmField.DismissText)
-			}
-		}
-	}
-}
-
 func TestOpsgenieTypeMatcher(t *testing.T) {
 	good := []string{"team", "user", "escalation", "schedule"}
 	for _, g := range good {
@@ -1077,10 +764,6 @@ parse_mode: invalid
 	}
 }
 
-func newBoolPointer(b bool) *bool {
-	return &b
-}
-
 func TestEmailConfig_UnmarshalYAML(t *testing.T) {
 	testConfig := []struct {
 		name     string
diff --git a/config/testdata/conf.slack-resolve-color-without-summary-header.yml b/config/testdata/conf.slack-resolve-color-without-summary-header.yml
new file mode 100644
index 0000000000..609b432d87
--- /dev/null
+++ b/config/testdata/conf.slack-resolve-color-without-summary-header.yml
@@ -0,0 +1,18 @@
+route:
+  receiver: 'slack-notifications'
+  group_by: [alertname]
+receivers:
+  - name: 'slack-notifications'
+    slack_configs:
+      - channel: '#alerts1'
+        text: 'test'
+        send_resolved: true
+        api_url: 'https://slack.com/api/chat.postMessage'
+        http_config:
+          authorization:
+            credentials: 'xoxb-XXXXXXXXXXXX-XXXXXXXXXXXX-XXXXXXXXXXXXXXXXXXXXXXXX'
+        message_strategy: thread
+        threaded_options:
+          use_summary_header: false
+          summary_header:
+            resolve_color: '#AAAAAA'
diff --git a/config/testdata/conf.slack-thread-message-and-webhook.yml b/config/testdata/conf.slack-thread-message-and-webhook.yml
new file mode 100644
index 0000000000..a326d54e98
--- /dev/null
+++ b/config/testdata/conf.slack-thread-message-and-webhook.yml
@@ -0,0 +1,11 @@
+route:
+  receiver: 'slack-notifications'
+  group_by: [alertname]
+receivers:
+  - name: 'slack-notifications'
+    slack_configs:
+      - channel: '#alerts1'
+        text: 'test'
+        send_resolved: true
+        api_url: 'https://hooks.slack.com/services/T00000000/B00000000/XXXXXXXXXXXXXXXXXXXXXXXX'
+        message_strategy: thread
diff --git a/config/testdata/conf.slack-thread-resolve-emoji-without-thread-message.yml b/config/testdata/conf.slack-thread-resolve-emoji-without-thread-message.yml
new file mode 100644
index 0000000000..2689fa952a
--- /dev/null
+++ b/config/testdata/conf.slack-thread-resolve-emoji-without-thread-message.yml
@@ -0,0 +1,15 @@
+route:
+  receiver: 'slack-notifications'
+  group_by: [alertname]
+receivers:
+  - name: 'slack-notifications'
+    slack_configs:
+      - channel: '#alerts1'
+        text: 'test'
+        send_resolved: true
+        api_url: 'https://slack.com/api/chat.postMessage'
+        http_config:
+          authorization:
+            credentials: 'xoxb-XXXXXXXXXXXX-XXXXXXXXXXXX-XXXXXXXXXXXXXXXXXXXXXXXX'
+        threaded_options:
+          resolve_emoji: 'white_check_mark'
diff --git a/config/testdata/conf.slack-thread-strategy-with-global-api-url.yml b/config/testdata/conf.slack-thread-strategy-with-global-api-url.yml
new file mode 100644
index 0000000000..5927949ff9
--- /dev/null
+++ b/config/testdata/conf.slack-thread-strategy-with-global-api-url.yml
@@ -0,0 +1,14 @@
+global:
+  slack_api_url: 'https://slack.com/api/chat.postMessage'
+route:
+  receiver: 'slack-notifications'
+  group_by: [alertname]
+receivers:
+  - name: 'slack-notifications'
+    slack_configs:
+      - channel: '#alerts'
+        text: 'test'
+        http_config:
+          authorization:
+            credentials: 'xoxb-test-token'
+        message_strategy: thread
diff --git a/config/testdata/conf.slack-thread-strategy-without-api-url.yml b/config/testdata/conf.slack-thread-strategy-without-api-url.yml
new file mode 100644
index 0000000000..c4e27376be
--- /dev/null
+++ b/config/testdata/conf.slack-thread-strategy-without-api-url.yml
@@ -0,0 +1,9 @@
+route:
+  receiver: 'slack-notifications'
+  group_by: [alertname]
+receivers:
+  - name: 'slack-notifications'
+    slack_configs:
+      - channel: '#alerts'
+        text: 'test'
+        message_strategy: thread
diff --git a/config/testdata/conf.slack-thread-update-parent-without-thread-message.yml b/config/testdata/conf.slack-thread-update-parent-without-thread-message.yml
new file mode 100644
index 0000000000..2689fa952a
--- /dev/null
+++ b/config/testdata/conf.slack-thread-update-parent-without-thread-message.yml
@@ -0,0 +1,15 @@
+route:
+  receiver: 'slack-notifications'
+  group_by: [alertname]
+receivers:
+  - name: 'slack-notifications'
+    slack_configs:
+      - channel: '#alerts1'
+        text: 'test'
+        send_resolved: true
+        api_url: 'https://slack.com/api/chat.postMessage'
+        http_config:
+          authorization:
+            credentials: 'xoxb-XXXXXXXXXXXX-XXXXXXXXXXXX-XXXXXXXXXXXXXXXXXXXXXXXX'
+        threaded_options:
+          resolve_emoji: 'white_check_mark'
diff --git a/config/testdata/conf.slack-update-message-and-webhook-with-new-field.yml b/config/testdata/conf.slack-update-message-and-webhook-with-new-field.yml
new file mode 100644
index 0000000000..4f4d2071ab
--- /dev/null
+++ b/config/testdata/conf.slack-update-message-and-webhook-with-new-field.yml
@@ -0,0 +1,13 @@
+route:
+  receiver: 'slack-notifications'
+  group_by: [alertname]
+receivers:
+  - name: 'slack-notifications'
+    slack_configs:
+      # use global
+      - channel: '#alerts1'
+        text: 'test'
+        send_resolved: true
+        # trying to use webhook urls with update_message
+        api_url: 'https://hooks.slack.com/services/T00000000/B00000000/XXXXXXXXXXXXXXXXXXXXXXXX'
+        message_strategy: update
diff --git a/docs/configuration.md b/docs/configuration.md
index 72cce8c2df..6a0d124716 100644
--- a/docs/configuration.md
+++ b/docs/configuration.md
@@ -1664,9 +1664,43 @@ fields:
 # NOTE: This will have no effect if set higher than the group_interval.
 [ timeout: <duration> | default = 0s ]
 
-# Enables updating existing Slack messages instead of creating new ones on alert state change.
-# Webhook URLs do not support updates.
-[ update_message: <boolean> | default = false ]
+# Controls how subsequent notifications for the same alert group are delivered.
+# "new" (default): each notification is a separate message.
+# "update": subsequent notifications update the original message in-place.
+# "thread": subsequent notifications are sent as threaded replies.
+# "update" and "thread" require api_url or api_url_file resolving to
+# https://slack.com/api/chat.postMessage (bot token).
+[ message_strategy: <string> | default = "new" ]
+
+# Limitation for "thread" (and "update"): thread metadata (for example the parent
+# message timestamp and channel id) is written to the notification log only after
+# the integration returns success for the entire notification attempt. If Slack
+# accepts an earlier API call in the same attempt but a later call fails and retries
+# are exhausted, the next flush may not see stored thread state and can open a new
+# thread in the channel, leaving the previous thread without further updates.
+
+# Options for threaded message behavior. Only valid when message_strategy is "thread".
+threaded_options:
+  # When true (default), the thread parent is a lightweight auto-updated summary
+  # header and all alert content is posted as replies. When false, the first
+  # alert message IS the thread parent and subsequent alerts are threaded replies.
+  [ use_summary_header: <boolean> | default = true ]
+
+  # Emoji name (without colons) to react with on the parent thread message
+  # when all alerts in the group are resolved (e.g. "white_check_mark").
+  # Requires the bot token to have reactions:write scope.
+  [ resolve_emoji: <string> ]
+
+  # Options that only apply when use_summary_header is true (default).
+  [ summary_header: <summary_header_thread_config> ]
+```
+
+#### `<summary_header_thread_config>`
+
+```yaml
+# Overrides the parent summary attachment color when all alerts resolve.
+# Supports Go templates.
+[ resolve_color: <tmpl_string> ]
 ```
 
 #### `<action_config>` (Slack)
diff --git a/notify/slack/config.go b/notify/slack/config.go
new file mode 100644
index 0000000000..7bf340f855
--- /dev/null
+++ b/notify/slack/config.go
@@ -0,0 +1,308 @@
+// Copyright The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package slack
+
+import (
+	"errors"
+	"fmt"
+	"time"
+
+	commoncfg "github.com/prometheus/common/config"
+
+	amcommoncfg "github.com/prometheus/alertmanager/config/common"
+)
+
+const (
+	// SlackMessageStrategyNew sends each notification as a separate message (default).
+	SlackMessageStrategyNew SlackMessageStrategy = "new"
+	// SlackMessageStrategyUpdate updates the original message in-place.
+	SlackMessageStrategyUpdate SlackMessageStrategy = "update"
+	// SlackMessageStrategyThread sends subsequent notifications as threaded replies.
+	SlackMessageStrategyThread SlackMessageStrategy = "thread"
+)
+
+// DefaultSlackConfig defines default values for Slack configurations.
+var DefaultSlackConfig = SlackConfig{
+	NotifierConfig: amcommoncfg.NotifierConfig{
+		VSendResolved: false,
+	},
+	Color:      `{{ template "slack.default.color" . }}`,
+	Username:   `{{ template "slack.default.username" . }}`,
+	Title:      `{{ template "slack.default.title" . }}`,
+	TitleLink:  `{{ template "slack.default.titlelink" . }}`,
+	IconEmoji:  `{{ template "slack.default.iconemoji" . }}`,
+	IconURL:    `{{ template "slack.default.iconurl" . }}`,
+	Pretext:    `{{ template "slack.default.pretext" . }}`,
+	Text:       `{{ template "slack.default.text" . }}`,
+	Fallback:   `{{ template "slack.default.fallback" . }}`,
+	CallbackID: `{{ template "slack.default.callbackid" . }}`,
+	Footer:     `{{ template "slack.default.footer" . }}`,
+}
+
+// SlackAction configures a single Slack action that is sent with each notification.
+// See https://api.slack.com/docs/message-attachments#action_fields and https://api.slack.com/docs/message-buttons
+// for more information.
+type SlackAction struct {
+	Type         string                  `yaml:"type,omitempty"  json:"type,omitempty"`
+	Text         string                  `yaml:"text,omitempty"  json:"text,omitempty"`
+	URL          string                  `yaml:"url,omitempty"   json:"url,omitempty"`
+	Style        string                  `yaml:"style,omitempty" json:"style,omitempty"`
+	Name         string                  `yaml:"name,omitempty"  json:"name,omitempty"`
+	Value        string                  `yaml:"value,omitempty"  json:"value,omitempty"`
+	ConfirmField *SlackConfirmationField `yaml:"confirm,omitempty"  json:"confirm,omitempty"`
+}
+
+// UnmarshalYAML implements the yaml.Unmarshaler interface for SlackAction.
+func (c *SlackAction) UnmarshalYAML(unmarshal func(any) error) error {
+	type plain SlackAction
+	if err := unmarshal((*plain)(c)); err != nil {
+		return err
+	}
+	if c.Type == "" {
+		return errors.New("missing type in Slack action configuration")
+	}
+	if c.Text == "" {
+		return errors.New("missing text in Slack action configuration")
+	}
+	if c.URL != "" {
+		// Clear all message action fields.
+		c.Name = ""
+		c.Value = ""
+		c.ConfirmField = nil
+	} else if c.Name != "" {
+		c.URL = ""
+	} else {
+		return errors.New("missing name or url in Slack action configuration")
+	}
+	return nil
+}
+
+// SlackConfirmationField protect users from destructive actions or particularly distinguished decisions
+// by asking them to confirm their button click one more time.
+// See https://api.slack.com/docs/interactive-message-field-guide#confirmation_fields for more information.
+type SlackConfirmationField struct {
+	Text        string `yaml:"text,omitempty"  json:"text,omitempty"`
+	Title       string `yaml:"title,omitempty"  json:"title,omitempty"`
+	OkText      string `yaml:"ok_text,omitempty"  json:"ok_text,omitempty"`
+	DismissText string `yaml:"dismiss_text,omitempty"  json:"dismiss_text,omitempty"`
+}
+
+// UnmarshalYAML implements the yaml.Unmarshaler interface for SlackConfirmationField.
+func (c *SlackConfirmationField) UnmarshalYAML(unmarshal func(any) error) error {
+	type plain SlackConfirmationField
+	if err := unmarshal((*plain)(c)); err != nil {
+		return err
+	}
+	if c.Text == "" {
+		return errors.New("missing text in Slack confirmation configuration")
+	}
+	return nil
+}
+
+// SlackField configures a single Slack field that is sent with each notification.
+// Each field must contain a title, value, and optionally, a boolean value to indicate if the field
+// is short enough to be displayed next to other fields designated as short.
+// See https://api.slack.com/docs/message-attachments#fields for more information.
+type SlackField struct {
+	Title string `yaml:"title,omitempty" json:"title,omitempty"`
+	Value string `yaml:"value,omitempty" json:"value,omitempty"`
+	Short *bool  `yaml:"short,omitempty" json:"short,omitempty"`
+}
+
+// UnmarshalYAML implements the yaml.Unmarshaler interface for SlackField.
+func (c *SlackField) UnmarshalYAML(unmarshal func(any) error) error {
+	type plain SlackField
+	if err := unmarshal((*plain)(c)); err != nil {
+		return err
+	}
+	if c.Title == "" {
+		return errors.New("missing title in Slack field configuration")
+	}
+	if c.Value == "" {
+		return errors.New("missing value in Slack field configuration")
+	}
+	return nil
+}
+
+// SlackMessageStrategy controls how subsequent notifications for the same
+// alert group are delivered to Slack.
+type SlackMessageStrategy string
+
+// SlackThreadedOptions configures thread-specific behavior when message_strategy is "thread".
+type SlackThreadedOptions struct {
+	// ResolveEmoji is the emoji name (without colons) to react with on the
+	// original thread message when all alerts in the group are resolved.
+	// Requires the bot token to have reactions:write scope.
+	ResolveEmoji string `yaml:"resolve_emoji,omitempty" json:"resolve_emoji,omitempty"`
+
+	// UseSummaryHeader controls whether the thread parent is a lightweight
+	// auto-updated summary (true, default) or the first actual alert message
+	// (false). When true, all alert content is posted as replies and the parent
+	// is continuously updated with the transition title and color.
+	UseSummaryHeader *bool `yaml:"use_summary_header,omitempty" json:"use_summary_header,omitempty"`
+
+	// SummaryHeader holds options for summary-header mode only (see UseSummaryHeader).
+	SummaryHeader *SlackThreadSummaryHeaderOptions `yaml:"summary_header,omitempty" json:"summary_header,omitempty"`
+}
+
+// SlackThreadSummaryHeaderOptions configures fields that only apply when
+// message_strategy is "thread" and use_summary_header is true (the lightweight
+// parent summary mode).
+type SlackThreadSummaryHeaderOptions struct {
+	// ResolveColor overrides the parent summary attachment color when the alert
+	// group resolves. Supports Go templates.
+	ResolveColor string `yaml:"resolve_color,omitempty" json:"resolve_color,omitempty"`
+}
+
+// SlackConfig configures notifications via Slack.
+type SlackConfig struct {
+	amcommoncfg.NotifierConfig `yaml:",inline" json:",inline"`
+
+	HTTPConfig *commoncfg.HTTPClientConfig `yaml:"http_config,omitempty" json:"http_config,omitempty"`
+
+	APIURL       *amcommoncfg.SecretURL `yaml:"api_url,omitempty" json:"api_url,omitempty"`
+	APIURLFile   string                 `yaml:"api_url_file,omitempty" json:"api_url_file,omitempty"`
+	AppToken     commoncfg.Secret       `yaml:"app_token,omitempty" json:"app_token,omitempty"`
+	AppTokenFile string                 `yaml:"app_token_file,omitempty" json:"app_token_file,omitempty"`
+	AppURL       *amcommoncfg.URL       `yaml:"app_url,omitempty" json:"app_url,omitempty"`
+
+	// Slack channel override, (like #other-channel or @username).
+	Channel  string `yaml:"channel,omitempty" json:"channel,omitempty"`
+	Username string `yaml:"username,omitempty" json:"username,omitempty"`
+	Color    string `yaml:"color,omitempty" json:"color,omitempty"`
+
+	Title       string         `yaml:"title,omitempty" json:"title,omitempty"`
+	TitleLink   string         `yaml:"title_link,omitempty" json:"title_link,omitempty"`
+	Pretext     string         `yaml:"pretext,omitempty" json:"pretext,omitempty"`
+	Text        string         `yaml:"text,omitempty" json:"text,omitempty"`
+	MessageText string         `yaml:"message_text,omitempty" json:"message_text,omitempty"`
+	Fields      []*SlackField  `yaml:"fields,omitempty" json:"fields,omitempty"`
+	ShortFields bool           `yaml:"short_fields" json:"short_fields,omitempty"`
+	Footer      string         `yaml:"footer,omitempty" json:"footer,omitempty"`
+	Fallback    string         `yaml:"fallback,omitempty" json:"fallback,omitempty"`
+	CallbackID  string         `yaml:"callback_id,omitempty" json:"callback_id,omitempty"`
+	IconEmoji   string         `yaml:"icon_emoji,omitempty" json:"icon_emoji,omitempty"`
+	IconURL     string         `yaml:"icon_url,omitempty" json:"icon_url,omitempty"`
+	ImageURL    string         `yaml:"image_url,omitempty" json:"image_url,omitempty"`
+	ThumbURL    string         `yaml:"thumb_url,omitempty" json:"thumb_url,omitempty"`
+	LinkNames   bool           `yaml:"link_names" json:"link_names,omitempty"`
+	MrkdwnIn    []string       `yaml:"mrkdwn_in,omitempty" json:"mrkdwn_in,omitempty"`
+	Actions     []*SlackAction `yaml:"actions,omitempty" json:"actions,omitempty"`
+
+	// MessageStrategy controls how subsequent notifications for the same alert
+	// group are delivered: "new" (default), "update" (edit in-place), or "thread"
+	// (threaded replies). "update" and "thread" require a bot token.
+	MessageStrategy SlackMessageStrategy `yaml:"message_strategy,omitempty" json:"message_strategy,omitempty"`
+
+	// UpdateMessage enables updating existing Slack messages instead of creating new ones.
+	// Deprecated: use message_strategy: update instead. If true, message_strategy must
+	// be unset or "update"; when message_strategy is unset it is treated as "update".
+	UpdateMessage bool `yaml:"update_message,omitempty" json:"update_message,omitempty"`
+
+	// ThreadedOptions configures thread-specific behavior.
+	// Only valid when message_strategy is "thread".
+	ThreadedOptions *SlackThreadedOptions `yaml:"threaded_options,omitempty" json:"threaded_options,omitempty"`
+	// Timeout is the maximum time allowed to invoke the slack. Setting this to 0
+	// does not impose a timeout.
+	Timeout time.Duration `yaml:"timeout" json:"timeout"`
+}
+
+// UnmarshalYAML implements the yaml.Unmarshaler interface.
+func (c *SlackConfig) UnmarshalYAML(unmarshal func(any) error) error {
+	*c = DefaultSlackConfig
+	type plain SlackConfig
+	if err := unmarshal((*plain)(c)); err != nil {
+		return err
+	}
+
+	if c.APIURL != nil && len(c.APIURLFile) > 0 {
+		return errors.New("at most one of api_url & api_url_file must be configured")
+	}
+	if c.AppToken != "" && len(c.AppTokenFile) > 0 {
+		return errors.New("at most one of app_token & app_token_file must be configured")
+	}
+	if (c.APIURL != nil || len(c.APIURLFile) > 0) && (c.AppToken != "" || len(c.AppTokenFile) > 0) {
+		return errors.New("at most one of api_url/api_url_file & app_token/app_token_file must be configured")
+	}
+
+	// Deprecated: remove this block when update_message is deleted.
+	if c.UpdateMessage {
+		if c.MessageStrategy != "" && c.MessageStrategy != SlackMessageStrategyUpdate {
+			return fmt.Errorf("update_message: true is incompatible with message_strategy %q; omit message_strategy or set message_strategy: \"update\"", c.MessageStrategy)
+		}
+		if c.MessageStrategy == "" {
+			c.MessageStrategy = SlackMessageStrategyUpdate
+		}
+	}
+	if c.MessageStrategy == "" {
+		c.MessageStrategy = SlackMessageStrategyNew
+	}
+
+	if c.MessageStrategy != SlackMessageStrategyNew &&
+		c.MessageStrategy != SlackMessageStrategyUpdate &&
+		c.MessageStrategy != SlackMessageStrategyThread {
+		return fmt.Errorf("unknown message_strategy %q; must be \"new\", \"update\", or \"thread\"", c.MessageStrategy)
+	}
+
+	if c.ThreadedOptions != nil {
+		if c.MessageStrategy != SlackMessageStrategyThread {
+			return errors.New("threaded_options requires message_strategy to be \"thread\"")
+		}
+		if c.ThreadedOptions.UseSummaryHeader != nil && !*c.ThreadedOptions.UseSummaryHeader && c.ThreadedOptions.SummaryHeader != nil {
+			return errors.New("threaded_options.summary_header requires use_summary_header to be enabled")
+		}
+	}
+
+	return nil
+}
+
+// ValidateMessageStrategy checks that the resolved api_url (after global defaults
+// have been applied) satisfies the requirements for update/thread strategies.
+func (c *SlackConfig) ValidateMessageStrategy() error {
+	switch c.MessageStrategy {
+	case SlackMessageStrategyUpdate, SlackMessageStrategyThread:
+		if c.APIURL == nil && c.APIURLFile == "" {
+			return fmt.Errorf("message_strategy %q requires api_url or api_url_file", c.MessageStrategy)
+		}
+		if c.APIURL != nil && c.APIURL.String() != "https://slack.com/api/chat.postMessage" {
+			return fmt.Errorf("message_strategy %q requires a bot token; api_url must be https://slack.com/api/chat.postMessage", c.MessageStrategy)
+		}
+	}
+	return nil
+}
+
+// UseSummaryHeaderInThread returns true when the thread parent should be a lightweight
+// auto-updated summary. Returns true by default (nil or explicit true).
+func (c *SlackConfig) UseSummaryHeaderInThread() bool {
+	if c.ThreadedOptions == nil || c.ThreadedOptions.UseSummaryHeader == nil {
+		return true
+	}
+	return *c.ThreadedOptions.UseSummaryHeader
+}
+
+// HasStrategyThatUpdatesParent reports whether message_strategy uses nflog to tie
+// multiple notifications to one Slack message or thread.
+func (c *SlackConfig) HasStrategyThatUpdatesParent() bool {
+	return c.HasUpdateStrategy() || c.HasThreadStrategy()
+}
+
+// HasUpdateStrategy is true when message_strategy is "update" (chat.update in place).
+func (c *SlackConfig) HasUpdateStrategy() bool {
+	return c.MessageStrategy == SlackMessageStrategyUpdate
+}
+
+// HasThreadStrategy is true when message_strategy is "thread" (threaded replies).
+func (c *SlackConfig) HasThreadStrategy() bool {
+	return c.MessageStrategy == SlackMessageStrategyThread
+}
diff --git a/notify/slack/config_test.go b/notify/slack/config_test.go
new file mode 100644
index 0000000000..61453a50b1
--- /dev/null
+++ b/notify/slack/config_test.go
@@ -0,0 +1,337 @@
+// Copyright The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package slack
+
+import (
+	"testing"
+
+	"gopkg.in/yaml.v2"
+)
+
+func TestLoadSlackConfiguration(t *testing.T) {
+	tests := []struct {
+		in       string
+		expected SlackConfig
+	}{
+		{
+			in: `
+color: green
+username: mark
+channel: engineering
+title_link: http://example.com/
+image_url: https://example.com/logo.png
+`,
+			expected: SlackConfig{
+				Color: "green", Username: "mark", Channel: "engineering",
+				TitleLink: "http://example.com/",
+				ImageURL:  "https://example.com/logo.png",
+			},
+		},
+		{
+			in: `
+color: green
+username: mark
+channel: alerts
+title_link: http://example.com/alert1
+mrkdwn_in:
+- pretext
+- text
+`,
+			expected: SlackConfig{
+				Color: "green", Username: "mark", Channel: "alerts",
+				MrkdwnIn: []string{"pretext", "text"}, TitleLink: "http://example.com/alert1",
+			},
+		},
+	}
+	for _, rt := range tests {
+		var cfg SlackConfig
+		err := yaml.UnmarshalStrict([]byte(rt.in), &cfg)
+		if err != nil {
+			t.Fatalf("\nerror returned when none expected, error:\n%v", err)
+		}
+		if rt.expected.Color != cfg.Color {
+			t.Errorf("\nexpected:\n%v\ngot:\n%v", rt.expected.Color, cfg.Color)
+		}
+		if rt.expected.Username != cfg.Username {
+			t.Errorf("\nexpected:\n%v\ngot:\n%v", rt.expected.Username, cfg.Username)
+		}
+		if rt.expected.Channel != cfg.Channel {
+			t.Errorf("\nexpected:\n%v\ngot:\n%v", rt.expected.Channel, cfg.Channel)
+		}
+		if rt.expected.ThumbURL != cfg.ThumbURL {
+			t.Errorf("\nexpected:\n%v\ngot:\n%v", rt.expected.ThumbURL, cfg.ThumbURL)
+		}
+		if rt.expected.TitleLink != cfg.TitleLink {
+			t.Errorf("\nexpected:\n%v\ngot:\n%v", rt.expected.TitleLink, cfg.TitleLink)
+		}
+		if rt.expected.ImageURL != cfg.ImageURL {
+			t.Errorf("\nexpected:\n%v\ngot:\n%v", rt.expected.ImageURL, cfg.ImageURL)
+		}
+		if len(rt.expected.MrkdwnIn) != len(cfg.MrkdwnIn) {
+			t.Errorf("\nexpected:\n%v\ngot:\n%v", rt.expected.MrkdwnIn, cfg.MrkdwnIn)
+		}
+		for i := range cfg.MrkdwnIn {
+			if rt.expected.MrkdwnIn[i] != cfg.MrkdwnIn[i] {
+				t.Errorf("\nexpected:\n%v\ngot:\n%v\nat index %v", rt.expected.MrkdwnIn[i], cfg.MrkdwnIn[i], i)
+			}
+		}
+	}
+}
+
+func TestSlackAuthMethodConfigValidation(t *testing.T) {
+	tests := []struct {
+		in          string
+		expectedErr string
+	}{
+		{
+			in: `
+api_url: 'https://hooks.slack.com/services/T00000000/B00000000/XXXXXXXXXXXXXXXXXXXXXXXX'
+api_url_file: /slack_url
+`,
+			expectedErr: "at most one of api_url & api_url_file must be configured",
+		},
+		{
+			in: `
+app_token: 'xoxb-1234-abcdefgh'
+app_token_file: /slack_app_token
+`,
+			expectedErr: "at most one of app_token & app_token_file must be configured",
+		},
+		{
+			in: `
+app_token: 'xoxb-1234-abcdefgh'
+api_url: 'https://hooks.slack.com/services/T00000000/B00000000/XXXXXXXXXXXXXXXXXXXXXXXX'
+`,
+			expectedErr: "at most one of api_url/api_url_file & app_token/app_token_file must be configured",
+		},
+	}
+
+	for _, rt := range tests {
+		var cfg SlackConfig
+		err := yaml.UnmarshalStrict([]byte(rt.in), &cfg)
+
+		// Check if an error occurred when it was NOT expected to.
+		if rt.expectedErr == "" && err != nil {
+			t.Fatalf("\nerror returned when none expected, error:\n%v", err)
+		}
+		// Check that an error occurred if one was expected to.
+		if rt.expectedErr != "" && err == nil {
+			t.Fatalf("\nno error returned, expected:\n%v", rt.expectedErr)
+		}
+		// Check that the error that occurred was what was expected.
+		if err != nil && err.Error() != rt.expectedErr {
+			t.Errorf("\nexpected:\n%v\ngot:\n%v", rt.expectedErr, err.Error())
+		}
+	}
+}
+
+func TestSlackFieldConfigValidation(t *testing.T) {
+	tests := []struct {
+		in       string
+		expected string
+	}{
+		{
+			in: `
+fields:
+- title: first
+  value: hello
+- title: second
+`,
+			expected: "missing value in Slack field configuration",
+		},
+		{
+			in: `
+fields:
+- title: first
+  value: hello
+  short: true
+- value: world
+  short: true
+`,
+			expected: "missing title in Slack field configuration",
+		},
+		{
+			in: `
+fields:
+- title: first
+  value: hello
+  short: true
+- title: second
+  value: world
+`,
+			expected: "",
+		},
+	}
+
+	for _, rt := range tests {
+		var cfg SlackConfig
+		err := yaml.UnmarshalStrict([]byte(rt.in), &cfg)
+
+		// Check if an error occurred when it was NOT expected to.
+		if rt.expected == "" && err != nil {
+			t.Fatalf("\nerror returned when none expected, error:\n%v", err)
+		}
+		// Check that an error occurred if one was expected to.
+		if rt.expected != "" && err == nil {
+			t.Fatalf("\nno error returned, expected:\n%v", rt.expected)
+		}
+		// Check that the error that occurred was what was expected.
+		if err != nil && err.Error() != rt.expected {
+			t.Errorf("\nexpected:\n%v\ngot:\n%v", rt.expected, err.Error())
+		}
+	}
+}
+
+func TestSlackFieldConfigUnmarshaling(t *testing.T) {
+	in := `
+fields:
+- title: first
+  value: hello
+  short: true
+- title: second
+  value: world
+- title: third
+  value: slack field test
+  short: false
+`
+	expected := []*SlackField{
+		{
+			Title: "first",
+			Value: "hello",
+			Short: newBoolPointer(true),
+		},
+		{
+			Title: "second",
+			Value: "world",
+			Short: nil,
+		},
+		{
+			Title: "third",
+			Value: "slack field test",
+			Short: newBoolPointer(false),
+		},
+	}
+
+	var cfg SlackConfig
+	err := yaml.UnmarshalStrict([]byte(in), &cfg)
+	if err != nil {
+		t.Fatalf("\nerror returned when none expected, error:\n%v", err)
+	}
+
+	for index, field := range cfg.Fields {
+		exp := expected[index]
+		if field.Title != exp.Title {
+			t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.Title, field.Title)
+		}
+		if field.Value != exp.Value {
+			t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.Value, field.Value)
+		}
+		if exp.Short == nil && field.Short != nil {
+			t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.Short, *field.Short)
+		}
+		if exp.Short != nil && field.Short == nil {
+			t.Errorf("\nexpected:\n%v\ngot:\n%v", *exp.Short, field.Short)
+		}
+		if exp.Short != nil && *exp.Short != *field.Short {
+			t.Errorf("\nexpected:\n%v\ngot:\n%v", *exp.Short, *field.Short)
+		}
+	}
+}
+
+func TestSlackActionsValidation(t *testing.T) {
+	in := `
+actions:
+- type: button
+  text: hello
+  url: https://localhost
+  style: danger
+- type: button
+  text: hello
+  name: something
+  style: default
+  confirm:
+    title: please confirm
+    text: are you sure?
+    ok_text: yes
+    dismiss_text: no
+`
+	expected := []*SlackAction{
+		{
+			Type:  "button",
+			Text:  "hello",
+			URL:   "https://localhost",
+			Style: "danger",
+		},
+		{
+			Type:  "button",
+			Text:  "hello",
+			Name:  "something",
+			Style: "default",
+			ConfirmField: &SlackConfirmationField{
+				Title:       "please confirm",
+				Text:        "are you sure?",
+				OkText:      "yes",
+				DismissText: "no",
+			},
+		},
+	}
+
+	var cfg SlackConfig
+	err := yaml.UnmarshalStrict([]byte(in), &cfg)
+	if err != nil {
+		t.Fatalf("\nerror returned when none expected, error:\n%v", err)
+	}
+
+	for index, action := range cfg.Actions {
+		exp := expected[index]
+		if action.Type != exp.Type {
+			t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.Type, action.Type)
+		}
+		if action.Text != exp.Text {
+			t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.Text, action.Text)
+		}
+		if action.URL != exp.URL {
+			t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.URL, action.URL)
+		}
+		if action.Style != exp.Style {
+			t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.Style, action.Style)
+		}
+		if action.Name != exp.Name {
+			t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.Name, action.Name)
+		}
+		if action.Value != exp.Value {
+			t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.Value, action.Value)
+		}
+		if action.ConfirmField != nil && exp.ConfirmField == nil || action.ConfirmField == nil && exp.ConfirmField != nil {
+			t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.ConfirmField, action.ConfirmField)
+		} else if action.ConfirmField != nil && exp.ConfirmField != nil {
+			if action.ConfirmField.Title != exp.ConfirmField.Title {
+				t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.ConfirmField.Title, action.ConfirmField.Title)
+			}
+			if action.ConfirmField.Text != exp.ConfirmField.Text {
+				t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.ConfirmField.Text, action.ConfirmField.Text)
+			}
+			if action.ConfirmField.OkText != exp.ConfirmField.OkText {
+				t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.ConfirmField.OkText, action.ConfirmField.OkText)
+			}
+			if action.ConfirmField.DismissText != exp.ConfirmField.DismissText {
+				t.Errorf("\nexpected:\n%v\ngot:\n%v", exp.ConfirmField.DismissText, action.ConfirmField.DismissText)
+			}
+		}
+	}
+}
+
+func newBoolPointer(b bool) *bool {
+	return &b
+}
diff --git a/notify/slack/internal/apiurl/apiurl.go b/notify/slack/internal/apiurl/apiurl.go
new file mode 100644
index 0000000000..29e4061965
--- /dev/null
+++ b/notify/slack/internal/apiurl/apiurl.go
@@ -0,0 +1,108 @@
+// Copyright The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Package apiurl resolves Slack notifier api_url / api_url_file into outbound HTTP URLs.
+package apiurl
+
+import (
+	"fmt"
+	"os"
+	"strings"
+
+	amcommoncfg "github.com/prometheus/alertmanager/config/common"
+)
+
+// Resolver turns Slack notifier config (api_url or api_url_file) into the actual HTTP
+// URL for each outgoing request (initial post, chat.update, etc.).
+type Resolver struct {
+	apiURL     *amcommoncfg.SecretURL
+	apiURLFile string
+}
+
+// NewResolver captures api_url / api_url_file from config when the notifier is built.
+//
+// APIURLFile is stored as a path only. The file is read from disk on every call to
+// URLForMethod when apiURL is nil—there is no in-memory cache of the URL string.
+// That way changes to the file (rotation, out-of-band updates) apply to the next
+// notification without restarting Alertmanager, matching historical behavior.
+func NewResolver(apiURL *amcommoncfg.SecretURL, apiURLFile string) *Resolver {
+	return &Resolver{apiURL: apiURL, apiURLFile: apiURLFile}
+}
+
+func (r *Resolver) URLForMethod(method string) (string, error) {
+	if method == "" {
+		if r.apiURL != nil {
+			apiURLStr := r.apiURL.String()
+			if apiURLStr != "" {
+				return apiURLStr, nil
+			}
+			return "", fmt.Errorf("slack api url is empty")
+		}
+
+		// Read api_url_file on each resolution; see New.
+		parsed, err := r.getURLFromFile()
+		if err != nil {
+			return "", err
+		}
+		return parsed.String(), nil
+	}
+
+	var baseURL *amcommoncfg.SecretURL
+	if r.apiURL != nil {
+		baseURL = r.apiURL
+	} else {
+		// Read api_url_file on each resolution; see New.
+		parsed, err := r.getURLFromFile()
+		if err != nil {
+			return "", err
+		}
+		secret := amcommoncfg.SecretURL(*parsed)
+		baseURL = &secret
+	}
+
+	return webAPIMethodURL(baseURL, method)
+}
+
+func (r *Resolver) getURLFromFile() (*amcommoncfg.URL, error) {
+	content, err := os.ReadFile(r.apiURLFile)
+	if err != nil {
+		return nil, err
+	}
+	raw := strings.TrimSpace(string(content))
+	return amcommoncfg.ParseURL(raw)
+}
+
+// webAPIMethodURL returns a Slack Web API URL for the given method, using the same
+// Scheme and host as postMessageURL. postMessageURL must be a URL whose path ends
+// with a method name (e.g. .../api/chat.postMessage).
+func webAPIMethodURL(postMessageURL *amcommoncfg.SecretURL, method string) (string, error) {
+	if postMessageURL == nil || postMessageURL.URL == nil {
+		return "", fmt.Errorf("slack api url is nil")
+	}
+
+	// Work on a copy so we never mutate the original URL.
+	u := *postMessageURL.URL
+	if u.Scheme == "" || u.Host == "" {
+		return "", fmt.Errorf("slack api url %q is missing scheme or host", u.String())
+	}
+
+	pathWithoutTrailingSlash := strings.TrimSuffix(u.Path, "/")
+	lastSlashIndex := strings.LastIndex(pathWithoutTrailingSlash, "/")
+	if lastSlashIndex < 0 {
+		return "", fmt.Errorf("slack api url %q has no path segment to replace", u.String())
+	}
+	u.Path = pathWithoutTrailingSlash[:lastSlashIndex+1] + method
+	u.RawQuery = ""
+	u.Fragment = ""
+	return u.String(), nil
+}
diff --git a/notify/slack/internal/apiurl/apiurl_test.go b/notify/slack/internal/apiurl/apiurl_test.go
new file mode 100644
index 0000000000..ac787ee0e5
--- /dev/null
+++ b/notify/slack/internal/apiurl/apiurl_test.go
@@ -0,0 +1,175 @@
+// Copyright The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package apiurl
+
+import (
+	"net/url"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	amcommoncfg "github.com/prometheus/alertmanager/config/common"
+)
+
+const (
+	baseURL                = "https://slack.com"
+	defaultURLWithAPIPath  = baseURL + "/api/chat.postMessage"
+	defaultURLWithFilePath = baseURL + "/file/chat.postMessage"
+
+	updateChatMethod = "chat.update"
+)
+
+func TestResolver_URLForMethod_ValidScenarios(t *testing.T) {
+	t.Parallel()
+
+	defaultAPIURLFile := createTempAPIURLFile(t, "test_url_for_method", defaultURLWithFilePath)
+
+	tests := []struct {
+		name       string
+		apiURL     *amcommoncfg.SecretURL
+		apiURLFile string
+		method     string
+		want       string
+	}{
+		{
+			name:       "empty method with apiURL",
+			apiURL:     getSecretURL(t, defaultURLWithAPIPath),
+			apiURLFile: "",
+			method:     "",
+			want:       defaultURLWithAPIPath,
+		},
+		{
+			name:       "empty method without apiURL but with apiURLFile",
+			apiURL:     nil,
+			apiURLFile: defaultAPIURLFile.Name(),
+			method:     "",
+			want:       defaultURLWithFilePath,
+		},
+		{
+			name:       "empty method with apiURL and apiURLFile, should use apiURL",
+			apiURL:     getSecretURL(t, defaultURLWithAPIPath),
+			apiURLFile: defaultAPIURLFile.Name(),
+			method:     "",
+			want:       defaultURLWithAPIPath,
+		},
+		{
+			name:       "method chat.update with apiURL",
+			apiURL:     getSecretURL(t, defaultURLWithAPIPath),
+			apiURLFile: defaultAPIURLFile.Name(),
+			method:     updateChatMethod,
+			want:       baseURL + "/api/" + updateChatMethod,
+		},
+		{
+			name:       "method chat.update with apiURL with trailing slash",
+			apiURL:     getSecretURL(t, defaultURLWithAPIPath+"/"),
+			apiURLFile: defaultAPIURLFile.Name(),
+			method:     updateChatMethod,
+			want:       baseURL + "/api/" + updateChatMethod,
+		},
+		{
+			name:       "method chat.update with apiURLFile",
+			apiURL:     nil,
+			apiURLFile: defaultAPIURLFile.Name(),
+			method:     updateChatMethod,
+			want:       baseURL + "/file/" + updateChatMethod,
+		},
+		{
+			name:       "method chat.update with apiURLFile with empty spaces",
+			apiURL:     nil,
+			apiURLFile: createTempAPIURLFile(t, "test_url_for_method_with_new_lines_and_spaces", defaultURLWithFilePath+"\n    \n").Name(),
+			method:     updateChatMethod,
+			want:       baseURL + "/file/" + updateChatMethod,
+		},
+		{
+			name:       "method chat.update with apiURLFile with trailing slash",
+			apiURL:     nil,
+			apiURLFile: createTempAPIURLFile(t, "test_url_for_method_with_trailing_slash", defaultURLWithFilePath+"/").Name(),
+			method:     updateChatMethod,
+			want:       baseURL + "/file/" + updateChatMethod,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			resolver := NewResolver(tt.apiURL, tt.apiURLFile)
+
+			got, err := resolver.URLForMethod(tt.method)
+			require.NoError(t, err)
+			require.Equal(t, tt.want, got)
+		})
+	}
+}
+
+func TestResolver_URLForMethod_InvalidScenarios(t *testing.T) {
+	t.Parallel()
+
+	invalidURL := amcommoncfg.SecretURL{
+		URL: &url.URL{},
+	}
+	tests := []struct {
+		name             string
+		apiURL           *amcommoncfg.SecretURL
+		apiURLFile       string
+		method           string
+		expectedErrorMsg string
+	}{
+		{
+			name:             "invalid URL",
+			apiURL:           &invalidURL,
+			apiURLFile:       "",
+			method:           "",
+			expectedErrorMsg: "slack api url is empty",
+		},
+		{
+			name:             "no apiURL nor apiURLFile",
+			apiURL:           nil,
+			apiURLFile:       "unknown",
+			method:           "",
+			expectedErrorMsg: "open unknown: no such file or directory",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			resolver := NewResolver(tt.apiURL, tt.apiURLFile)
+
+			_, err := resolver.URLForMethod(tt.method)
+			require.Error(t, err)
+			require.Contains(t, err.Error(), tt.expectedErrorMsg)
+		})
+	}
+}
+
+func getSecretURL(t *testing.T, raw string) *amcommoncfg.SecretURL {
+	t.Helper()
+	u, err := amcommoncfg.ParseURL(raw)
+	require.NoError(t, err)
+	s := amcommoncfg.SecretURL(*u)
+	return &s
+}
+
+func createTempAPIURLFile(t *testing.T, pattern, url string) *os.File {
+	t.Helper()
+	apiURLFileWithNewLines, err := os.CreateTemp(t.TempDir(), pattern)
+	require.NoError(t, err)
+	_, err = apiURLFileWithNewLines.WriteString(url)
+	require.NoError(t, err)
+	require.NoError(t, apiURLFileWithNewLines.Close())
+	return apiURLFileWithNewLines
+}
diff --git a/notify/slack/slack.go b/notify/slack/slack.go
index dbcea63dd7..5696ec9fbe 100644
--- a/notify/slack/slack.go
+++ b/notify/slack/slack.go
@@ -21,14 +21,13 @@ import (
 	"io"
 	"log/slog"
 	"net/http"
-	"os"
 	"strings"
 
 	commoncfg "github.com/prometheus/common/config"
 
-	"github.com/prometheus/alertmanager/config"
 	"github.com/prometheus/alertmanager/nflog"
 	"github.com/prometheus/alertmanager/notify"
+	"github.com/prometheus/alertmanager/notify/slack/internal/apiurl"
 	"github.com/prometheus/alertmanager/template"
 	"github.com/prometheus/alertmanager/types"
 )
@@ -36,19 +35,8 @@ import (
 // https://api.slack.com/reference/messaging/attachments#legacy_fields - 1024, no units given, assuming runes or characters.
 const maxTitleLenRunes = 1024
 
-// Notifier implements a Notifier for Slack notifications.
-type Notifier struct {
-	conf    *config.SlackConfig
-	tmpl    *template.Template
-	logger  *slog.Logger
-	client  *http.Client
-	retrier *notify.Retrier
-
-	postJSONFunc func(ctx context.Context, client *http.Client, url string, body io.Reader) (*http.Response, error)
-}
-
 // New returns a new Slack notification handler.
-func New(c *config.SlackConfig, t *template.Template, l *slog.Logger, httpOpts ...commoncfg.HTTPClientOption) (*Notifier, error) {
+func New(c *SlackConfig, t *template.Template, l *slog.Logger, httpOpts ...commoncfg.HTTPClientOption) (*Notifier, error) {
 	client, err := notify.NewClientWithTracing(*c.HTTPConfig, "slack", httpOpts...)
 	if err != nil {
 		return nil, err
@@ -60,47 +48,11 @@ func New(c *config.SlackConfig, t *template.Template, l *slog.Logger, httpOpts .
 		logger:       l,
 		client:       client,
 		retrier:      &notify.Retrier{},
+		urlResolver:  apiurl.NewResolver(c.APIURL, c.APIURLFile),
 		postJSONFunc: notify.PostJSON,
 	}, nil
 }
 
-// request is the request for sending a slack notification.
-type request struct {
-	Channel     string       `json:"channel,omitempty"`
-	Timestamp   string       `json:"ts,omitempty"`
-	Username    string       `json:"username,omitempty"`
-	IconEmoji   string       `json:"icon_emoji,omitempty"`
-	IconURL     string       `json:"icon_url,omitempty"`
-	LinkNames   bool         `json:"link_names,omitempty"`
-	Text        string       `json:"text,omitempty"`
-	Attachments []attachment `json:"attachments"`
-}
-
-// attachment is used to display a richly-formatted message block.
-type attachment struct {
-	Title      string               `json:"title,omitempty"`
-	TitleLink  string               `json:"title_link,omitempty"`
-	Pretext    string               `json:"pretext,omitempty"`
-	Text       string               `json:"text"`
-	Fallback   string               `json:"fallback"`
-	CallbackID string               `json:"callback_id"`
-	Fields     []config.SlackField  `json:"fields,omitempty"`
-	Actions    []config.SlackAction `json:"actions,omitempty"`
-	ImageURL   string               `json:"image_url,omitempty"`
-	ThumbURL   string               `json:"thumb_url,omitempty"`
-	Footer     string               `json:"footer"`
-	Color      string               `json:"color,omitempty"`
-	MrkdwnIn   []string             `json:"mrkdwn_in,omitempty"`
-}
-
-// slackResponse represents the response from Slack API.
-type slackResponse struct {
-	OK        bool   `json:"ok"`
-	Error     string `json:"error,omitempty"`
-	Channel   string `json:"channel,omitempty"`
-	Timestamp string `json:"ts,omitempty"`
-}
-
 // Notify implements the Notifier interface.
 func (n *Notifier) Notify(ctx context.Context, as ...*types.Alert) (bool, error) {
 	var err error
@@ -143,7 +95,7 @@ func (n *Notifier) Notify(ctx context.Context, as ...*types.Alert) (bool, error)
 
 	numFields := len(n.conf.Fields)
 	if numFields > 0 {
-		fields := make([]config.SlackField, numFields)
+		fields := make([]SlackField, numFields)
 		for index, field := range n.conf.Fields {
 			// Check if short was defined for the field otherwise fallback to the global setting
 			var short bool
@@ -154,7 +106,7 @@ func (n *Notifier) Notify(ctx context.Context, as ...*types.Alert) (bool, error)
 			}
 
 			// Rebuild the field by executing any templates and setting the new value for short
-			fields[index] = config.SlackField{
+			fields[index] = SlackField{
 				Title: tmplText(field.Title),
 				Value: tmplText(field.Value),
 				Short: &short,
@@ -165,9 +117,9 @@ func (n *Notifier) Notify(ctx context.Context, as ...*types.Alert) (bool, error)
 
 	numActions := len(n.conf.Actions)
 	if numActions > 0 {
-		actions := make([]config.SlackAction, numActions)
+		actions := make([]SlackAction, numActions)
 		for index, action := range n.conf.Actions {
-			slackAction := config.SlackAction{
+			slackAction := SlackAction{
 				Type:  tmplText(action.Type),
 				Text:  tmplText(action.Text),
 				URL:   tmplText(action.URL),
@@ -177,7 +129,7 @@ func (n *Notifier) Notify(ctx context.Context, as ...*types.Alert) (bool, error)
 			}
 
 			if action.ConfirmField != nil {
-				slackAction.ConfirmField = &config.SlackConfirmationField{
+				slackAction.ConfirmField = &SlackConfirmationField{
 					Title:       tmplText(action.ConfirmField.Title),
 					Text:        tmplText(action.ConfirmField.Text),
 					OkText:      tmplText(action.ConfirmField.OkText),
@@ -190,15 +142,9 @@ func (n *Notifier) Notify(ctx context.Context, as ...*types.Alert) (bool, error)
 		att.Actions = actions
 	}
 
-	var u string
-	if n.conf.APIURL != nil {
-		u = n.conf.APIURL.String()
-	} else {
-		content, err := os.ReadFile(n.conf.APIURLFile)
-		if err != nil {
-			return false, err
-		}
-		u = strings.TrimSpace(string(content))
+	u, err := n.urlResolver.URLForMethod("")
+	if err != nil {
+		return false, err
 	}
 
 	if n.conf.Timeout > 0 {
@@ -231,7 +177,11 @@ func (n *Notifier) Notify(ctx context.Context, as ...*types.Alert) (bool, error)
 			channelId, _ := store.GetStr("channelId")
 			logger.Debug("attempt recovering threadTs and channelId to update an existing message", "threadTs", threadTs, "channelId", channelId)
 			if threadTs != "" && channelId != "" {
-				u = "https://slack.com/api/chat.update"
+				updateURL, err := n.urlResolver.URLForMethod("chat.update")
+				if err != nil {
+					return false, err
+				}
+				u = updateURL
 				req.Timestamp = threadTs
 				req.Channel = channelId
 				logger.Debug("updating previously sent message", "threadTs", threadTs, "channelId", channelId)
diff --git a/notify/slack/slack_test.go b/notify/slack/slack_test.go
index 68924f7075..4a00f4b24f 100644
--- a/notify/slack/slack_test.go
+++ b/notify/slack/slack_test.go
@@ -21,7 +21,6 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"net/url"
-	"os"
 	"strings"
 	"testing"
 	"time"
@@ -33,7 +32,6 @@ import (
 
 	amcommoncfg "github.com/prometheus/alertmanager/config/common"
 
-	"github.com/prometheus/alertmanager/config"
 	"github.com/prometheus/alertmanager/notify"
 	"github.com/prometheus/alertmanager/notify/test"
 	"github.com/prometheus/alertmanager/template"
@@ -42,7 +40,7 @@ import (
 
 func TestSlackRetry(t *testing.T) {
 	notifier, err := New(
-		&config.SlackConfig{
+		&SlackConfig{
 			HTTPConfig: &commoncfg.HTTPClientConfig{},
 		},
 		test.CreateTmpl(t),
@@ -61,7 +59,7 @@ func TestSlackRedactedURL(t *testing.T) {
 	defer fn()
 
 	notifier, err := New(
-		&config.SlackConfig{
+		&SlackConfig{
 			APIURL:     &amcommoncfg.SecretURL{URL: u},
 			HTTPConfig: &commoncfg.HTTPClientConfig{},
 		},
@@ -73,50 +71,6 @@ func TestSlackRedactedURL(t *testing.T) {
 	test.AssertNotifyLeaksNoSecret(ctx, t, notifier, u.String())
 }
 
-func TestGettingSlackURLFromFile(t *testing.T) {
-	ctx, u, fn := test.GetContextWithCancelingURL()
-	defer fn()
-
-	f, err := os.CreateTemp(t.TempDir(), "slack_test")
-	require.NoError(t, err, "creating temp file failed")
-	_, err = f.WriteString(u.String())
-	require.NoError(t, err, "writing to temp file failed")
-
-	notifier, err := New(
-		&config.SlackConfig{
-			APIURLFile: f.Name(),
-			HTTPConfig: &commoncfg.HTTPClientConfig{},
-		},
-		test.CreateTmpl(t),
-		promslog.NewNopLogger(),
-	)
-	require.NoError(t, err)
-
-	test.AssertNotifyLeaksNoSecret(ctx, t, notifier, u.String())
-}
-
-func TestTrimmingSlackURLFromFile(t *testing.T) {
-	ctx, u, fn := test.GetContextWithCancelingURL()
-	defer fn()
-
-	f, err := os.CreateTemp(t.TempDir(), "slack_test_newline")
-	require.NoError(t, err, "creating temp file failed")
-	_, err = f.WriteString(u.String() + "\n\n")
-	require.NoError(t, err, "writing to temp file failed")
-
-	notifier, err := New(
-		&config.SlackConfig{
-			APIURLFile: f.Name(),
-			HTTPConfig: &commoncfg.HTTPClientConfig{},
-		},
-		test.CreateTmpl(t),
-		promslog.NewNopLogger(),
-	)
-	require.NoError(t, err)
-
-	test.AssertNotifyLeaksNoSecret(ctx, t, notifier, u.String())
-}
-
 func TestNotifier_Notify_WithReason(t *testing.T) {
 	tests := []struct {
 		name           string
@@ -196,7 +150,7 @@ func TestNotifier_Notify_WithReason(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			apiurl, _ := url.Parse("https://slack.com/post.Message")
 			notifier, err := New(
-				&config.SlackConfig{
+				&SlackConfig{
 					NotifierConfig: amcommoncfg.NotifierConfig{},
 					HTTPConfig:     &commoncfg.HTTPClientConfig{},
 					APIURL:         &amcommoncfg.SecretURL{URL: apiurl},
@@ -254,7 +208,7 @@ func TestSlackTimeout(t *testing.T) {
 		t.Run(name, func(t *testing.T) {
 			u, _ := url.Parse("https://slack.com/post.Message")
 			notifier, err := New(
-				&config.SlackConfig{
+				&SlackConfig{
 					NotifierConfig: amcommoncfg.NotifierConfig{},
 					HTTPConfig:     &commoncfg.HTTPClientConfig{},
 					APIURL:         &amcommoncfg.SecretURL{URL: u},
@@ -325,7 +279,7 @@ func TestSlackMessageField(t *testing.T) {
 
 	// 4. Configure Notifier with BOTH new and old fields
 	u, _ := url.Parse(server.URL)
-	conf := &config.SlackConfig{
+	conf := &SlackConfig{
 		APIURL:      &amcommoncfg.SecretURL{URL: u},
 		MessageText: "My Top Level Message", // Your NEW field
 		Title:       "Old Attachment Title", // An OLD field
diff --git a/notify/slack/types.go b/notify/slack/types.go
new file mode 100644
index 0000000000..550fc7d595
--- /dev/null
+++ b/notify/slack/types.go
@@ -0,0 +1,74 @@
+// Copyright The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package slack
+
+import (
+	"context"
+	"io"
+	"log/slog"
+	"net/http"
+
+	"github.com/prometheus/alertmanager/notify"
+	"github.com/prometheus/alertmanager/notify/slack/internal/apiurl"
+	"github.com/prometheus/alertmanager/template"
+)
+
+// Notifier implements a Notifier for Slack notifications.
+type Notifier struct {
+	conf        *SlackConfig
+	tmpl        *template.Template
+	logger      *slog.Logger
+	client      *http.Client
+	retrier     *notify.Retrier
+	urlResolver *apiurl.Resolver
+
+	postJSONFunc func(ctx context.Context, client *http.Client, url string, body io.Reader) (*http.Response, error)
+}
+
+// request is the request for sending a Slack notification.
+type request struct {
+	Channel     string       `json:"channel,omitempty"`
+	Timestamp   string       `json:"ts,omitempty"`
+	Username    string       `json:"username,omitempty"`
+	IconEmoji   string       `json:"icon_emoji,omitempty"`
+	IconURL     string       `json:"icon_url,omitempty"`
+	LinkNames   bool         `json:"link_names,omitempty"`
+	Text        string       `json:"text,omitempty"`
+	Attachments []attachment `json:"attachments"`
+}
+
+// attachment is used to display a richly formatted message block.
+type attachment struct {
+	Title      string        `json:"title,omitempty"`
+	TitleLink  string        `json:"title_link,omitempty"`
+	Pretext    string        `json:"pretext,omitempty"`
+	Text       string        `json:"text"`
+	Fallback   string        `json:"fallback"`
+	CallbackID string        `json:"callback_id"`
+	Fields     []SlackField  `json:"fields,omitempty"`
+	Actions    []SlackAction `json:"actions,omitempty"`
+	ImageURL   string        `json:"image_url,omitempty"`
+	ThumbURL   string        `json:"thumb_url,omitempty"`
+	Footer     string        `json:"footer"`
+	Color      string        `json:"color,omitempty"`
+	MrkdwnIn   []string      `json:"mrkdwn_in,omitempty"`
+}
+
+// slackResponse represents the response from Slack API.
+type slackResponse struct {
+	OK        bool   `json:"ok"`
+	Error     string `json:"error,omitempty"`
+	Channel   string `json:"channel,omitempty"`
+	Timestamp string `json:"ts,omitempty"`
+}