diff --git a/apps/api/src/app/api/integrations/slack/constants.ts b/apps/api/src/app/api/integrations/slack/constants.ts
index a71120bc0a2..8d30e7a46ad 100644
--- a/apps/api/src/app/api/integrations/slack/constants.ts
+++ b/apps/api/src/app/api/integrations/slack/constants.ts
@@ -1,4 +1,5 @@
 export const SLACK_MODELS = [
+	{ value: "claude-sonnet-5-5", label: "Sonnet 5.5" },
 	{ value: "claude-sonnet-5", label: "Sonnet 5" },
 	{ value: "claude-sonnet-4-6", label: "Sonnet 4.6" },
 	{ value: "claude-opus-5", label: "Opus 5" },
diff --git a/apps/api/src/app/api/integrations/slack/events/utils/run-agent/run-agent.ts b/apps/api/src/app/api/integrations/slack/events/utils/run-agent/run-agent.ts
index c6df617ea02..63a2274ab14 100644
--- a/apps/api/src/app/api/integrations/slack/events/utils/run-agent/run-agent.ts
+++ b/apps/api/src/app/api/integrations/slack/events/utils/run-agent/run-agent.ts
@@ -920,6 +920,7 @@ ${agentContext}`;
 						},
 					],
 					...([
+						"claude-sonnet-5-5",
 						"claude-sonnet-5",
 						"claude-sonnet-4-6",
 						"claude-opus-5",
diff --git a/packages/shared/src/agent-models.test.ts b/packages/shared/src/agent-models.test.ts
index d6721418601..8f0fb7b9920 100644
--- a/packages/shared/src/agent-models.test.ts
+++ b/packages/shared/src/agent-models.test.ts
@@ -596,20 +596,24 @@ describe("buildAgentModelEnv (vibe)", () => {
 describe("September 2026 model launches", () => {
 	it.each([
 		["claude", "claude-opus-5-5"],
+		["claude", "claude-sonnet-5-5"],
 		["codex", "gpt-6-astra"],
 		["codex", "gpt-6-sol"],
 		["codex", "gpt-6-luna"],
 		["copilot", "claude-opus-5.5"],
 		["copilot", "claude-fable-5.1"],
+		["copilot", "claude-sonnet-5.5"],
 		["copilot", "gpt-6-astra"],
 		["copilot", "gpt-6-sol"],
 		["copilot", "gpt-6-luna"],
 		["gemini", "gemini-3.8-flash"],
 		["gemini", "gemini-3.1-pro-preview"],
 		["opencode", "anthropic/claude-opus-5-5"],
+		["opencode", "anthropic/claude-sonnet-5-5"],
 		["opencode", "anthropic/claude-sonnet-5"],
 		["opencode", "google/gemini-3.8-flash"],
 		["omp", "anthropic/claude-opus-5-5"],
+		["omp", "anthropic/claude-sonnet-5-5"],
 		["omp", "anthropic/claude-sonnet-5"],
 	])("launches %s with its exact model id %s", (preset, model) => {
 		expect(isCuratedAgentModel(preset, model)).toBe(true);
@@ -647,11 +651,15 @@ describe("September 2026 model launches", () => {
 		}
 	});
 
-	it("offers Sonnet 5 in the cloud chat catalog", () => {
-		expect(
-			SUPERSET_CHAT_MODELS.find(({ id }) => id === "anthropic/claude-sonnet-5")
-				?.provider,
-		).toBe("Anthropic");
+	it("offers Sonnet 5.5 and Sonnet 5 in the cloud chat catalog", () => {
+		for (const id of [
+			"anthropic/claude-sonnet-5-5",
+			"anthropic/claude-sonnet-5",
+		]) {
+			expect(
+				SUPERSET_CHAT_MODELS.find((model) => model.id === id)?.provider,
+			).toBe("Anthropic");
+		}
 	});
 
 	it("has unique ids within every agent catalog", () => {
diff --git a/packages/shared/src/agent-models.ts b/packages/shared/src/agent-models.ts
index e96068c2e33..199d6733449 100644
--- a/packages/shared/src/agent-models.ts
+++ b/packages/shared/src/agent-models.ts
@@ -82,6 +82,11 @@ export const SUPERSET_CHAT_MODELS: readonly SupersetChatModel[] = [
 		provider: "Anthropic",
 	},
 	{ id: "anthropic/claude-fable-5", label: "Fable 5", provider: "Anthropic" },
+	{
+		id: "anthropic/claude-sonnet-5-5",
+		label: "Sonnet 5.5",
+		provider: "Anthropic",
+	},
 	{ id: "anthropic/claude-sonnet-5", label: "Sonnet 5", provider: "Anthropic" },
 	{
 		id: "anthropic/claude-sonnet-4-6",
@@ -131,6 +136,7 @@ export const AGENT_MODEL_SUPPORT: readonly AgentModelSupport[] = [
 			{ id: "claude-fable-5", label: "Fable 5", group: PINNED_GROUP },
 			{ id: "claude-opus-5-5", label: "Opus 5.5", group: PINNED_GROUP },
 			{ id: "claude-opus-5", label: "Opus 5", group: PINNED_GROUP },
+			{ id: "claude-sonnet-5-5", label: "Sonnet 5.5", group: PINNED_GROUP },
 			{ id: "claude-sonnet-5", label: "Sonnet 5", group: PINNED_GROUP },
 			{ id: "claude-opus-4-8", label: "Opus 4.8", group: PINNED_GROUP },
 			{ id: "claude-opus-4-7", label: "Opus 4.7", group: PINNED_GROUP },
@@ -175,6 +181,7 @@ export const AGENT_MODEL_SUPPORT: readonly AgentModelSupport[] = [
 			{ id: "claude-opus-5.5", label: "Claude Opus 5.5" },
 			{ id: "claude-opus-5", label: "Claude Opus 5" },
 			{ id: "claude-fable-5.1", label: "Claude Fable 5.1" },
+			{ id: "claude-sonnet-5.5", label: "Claude Sonnet 5.5" },
 			{ id: "claude-sonnet-5", label: "Claude Sonnet 5" },
 			{ id: "claude-sonnet-4.6", label: "Claude Sonnet 4.6" },
 			{ id: "claude-haiku-4.5", label: "Claude Haiku 4.5" },
@@ -297,6 +304,7 @@ export const AGENT_MODEL_SUPPORT: readonly AgentModelSupport[] = [
 			// models.dev directly (2026-09-01), the gpt-6 family likewise
 			// (2026-09-23).
 			{ id: "anthropic/claude-opus-5-5", label: "Claude Opus 5.5" },
+			{ id: "anthropic/claude-sonnet-5-5", label: "Claude Sonnet 5.5" },
 			{ id: "anthropic/claude-sonnet-5", label: "Claude Sonnet 5" },
 			{ id: "anthropic/claude-opus-5", label: "Claude Opus 5" },
 			{ id: "anthropic/claude-fable-5-1", label: "Claude Fable 5.1" },
@@ -325,6 +333,7 @@ export const AGENT_MODEL_SUPPORT: readonly AgentModelSupport[] = [
 			{ id: "@slow", label: "Configured slow model" },
 			{ id: "@plan", label: "Configured plan model" },
 			{ id: "anthropic/claude-opus-5-5", label: "Claude Opus 5.5" },
+			{ id: "anthropic/claude-sonnet-5-5", label: "Claude Sonnet 5.5" },
 			{ id: "anthropic/claude-sonnet-5", label: "Claude Sonnet 5" },
 			{ id: "anthropic/claude-opus-5", label: "Claude Opus 5" },
 			{ id: "anthropic/claude-fable-5-1", label: "Claude Fable 5.1" },