feat(coding-agent): default Anthropic model is Claude Opus 5.5

packages/coding-agent/CHANGELOG.md

@@ -12,6 +12,10 @@
 - Anthropic sessions now use message threads: each request sends only the new messages and the server continues from the previous reply, falling back to the full request when the conversation changed (for example after compaction or a tool list change). On by default for the `anthropic` provider on `api.anthropic.com`; set `compat.supportsMessageThreads` in `models.json` to enable it for gateways that forward the `thread` field, or to turn it off. Cache warming does not touch the session's thread ([#11545](https://github.com/earendil-works/pi/pull/11545))
 - `pi.registerMarkdownTransformer()` takes an optional `{ messageTypes }` that selects the Markdown surfaces a transformer runs on. Besides user, assistant, and thinking Markdown, transformers can now opt into `custom` (custom messages and skill blocks), `summary` (branch and compaction summaries), and `changelog` (What's New, `/changelog`, the Extension Updates notice, and the Update Available note). Without options a transformer runs on user, assistant, and thinking Markdown as before. The built-in Mermaid renderer now also draws diagrams in expanded branch and compaction summaries
 
+### Changed
+
+- The default model for the `anthropic` provider is now Claude Opus 5.5 (`claude-opus-5-5`) instead of Claude Opus 4.8
+
 ### Fixed
 
 - Images in steering and follow-up messages, including `prompt()` while streaming, are now resized like images in idle prompts instead of being sent and saved at full size ([#11738](https://github.com/earendil-works/pi/issues/11738))

packages/coding-agent/src/core/model-resolver.ts

@@ -20,7 +20,7 @@ import type { ModelRuntime } from "./model-runtime.ts";
 export const defaultModelPerProvider: Partial<Record<KnownProvider, string>> = {
 	"amazon-bedrock": "us.anthropic.claude-opus-4-6-v1",
 	"ant-ling": "Ring-2.6-1T",
-	anthropic: "claude-opus-4-8",
+	anthropic: "claude-opus-5-5",
 	openai: "gpt-6.1-sol",
 	azure: "gpt-5.4",
 	"openai-codex": "gpt-6.1-sol",

packages/coding-agent/test/model-resolver.test.ts

@@ -730,6 +730,10 @@ describe("default model selection", () => {
 		expect(defaultModelPerProvider["vercel-ai-gateway"]).toBe("zai/glm-5.1");
 	});
 
+	test("anthropic default tracks current model", () => {
+		expect(defaultModelPerProvider.anthropic).toBe("claude-opus-5-5");
+	});
+
 	test("xai default tracks current model", () => {
 		expect(defaultModelPerProvider.xai).toBe("grok-4.7");
 	});