fix(ai): make Claude capability defaults forward-compatible (#52535)

packages/ai/src/protocols/anthropic-messages.ts

@@ -807,15 +807,12 @@ const requireThinkingSignature = (request: LLMRequest) => {
 // Mid-conversation system messages became available with Opus 4.8 and version
 // 5 of the other supported Claude families. Treat later family versions as
 // compatible without assuming that every Anthropic Messages model is Claude.
+// Opus 4.8 and every Claude 5 model accept mid-conversation system messages; later versions inherit support.
 const supportsNativeSystemUpdates = (request: LLMRequest) => {
-  const match = /(?:^|[./])claude-(fable|haiku|mythos|opus|sonnet)-(\d+)(?:[.-](\d+))?/.exec(
-    String(request.model.id).toLowerCase(),
-  )
-  if (!match) return false
-  const major = Number(match[2])
-  if (match[1] !== "opus") return major >= 5
-  if (major !== 4) return major >= 5
-  return match[3] !== undefined && match[3].length <= 2 && Number(match[3]) >= 8
+  const version = claudeVersion(String(request.model.id))
+  if (version === undefined) return false
+  if (version.family === "opus" && version.major === 4) return version.minor >= 8
+  return version.major >= 5
 }
 
 const endsInServerToolUse = (message: LLMRequest["messages"][number]) => {
@@ -992,13 +989,13 @@ const lowerMessages = Effect.fn("AnthropicMessages.lowerMessages")(function* (
   return messages
 })
 
+// Per-turn effort started with Claude Opus 5 and every Claude 5.1 model; later versions of any family inherit it.
 const supportsEffortUpdates = (model: LLMRequest["model"]) => {
   const override = model.compatibility?.supportsEffortUpdates
   if (override !== undefined) return override
   const version = claudeVersion(model.id)
   if (version === undefined) return false
-  if (version.family === "opus") return version.major >= 5
-  if (version.family !== "fable" && version.family !== "mythos") return false
+  if (version.family === "opus" && version.major >= 5) return true
   return version.major > 5 || (version.major === 5 && version.minor >= 1)
 }
 

packages/ai/test/effort-updates.test.ts

@@ -197,9 +197,15 @@ describe("Anthropic Messages effort updates", () => {
     ["anthropic/claude-opus-5", true],
     ["claude-fable-5-1", true],
     ["claude-mythos-5-1", true],
+    ["claude-opus-5-5", true],
+    ["claude-sonnet-5-5", true],
+    ["anthropic/claude-sonnet-5-5", true],
+    ["claude-sonnet-6", true],
+    ["claude-haiku-6", true],
     ["claude-fable-5", false],
     ["claude-opus-4-8", false],
     ["claude-sonnet-5", false],
+    ["claude-sonnet-5-20260801", false],
     ["kimi-k2.5", false],
   ] as const) {
     it.effect(`${supported ? "lowers" : "strips"} markers for ${id}`, () =>

packages/ai/test/provider/anthropic-messages.test.ts

@@ -314,6 +314,9 @@ describe("Anthropic Messages route", () => {
         "claude-haiku-5-1",
         "claude-fable-6",
         "anthropic/claude-mythos-7.2",
+        "claude-sonnet-5-5",
+        "claude-opus-4-8@20260101",
+        "claude-nova-6",
       ]
 
       const prepared = yield* Effect.forEach(ids, (id) =>