Update claude-api skill: Claude Opus 5 (#1476)

* Update claude-api skill: Claude Opus 5

- Add Claude Opus 5 (`claude-opus-5`) as the default model across all
  SDK examples, model tables, pricing, and migration guidance.
- Add an Opus 5 migration section covering the API changes that come
  with it, and move Opus 4.8 into the previous-generation slot.
- Drop the Opus 4.7 fast-mode guidance, which no longer applies.
- Scope the server-side fallbacks beta header to the current version.

* Update claude-api skill: Opus 5 fast-follow corrections

- Server-side refusal fallbacks are available on Claude Platform on AWS,
  not just the Claude API. Correct the availability statements in
  SKILL.md, the migration guide, and the platform-availability table.
- Simplify the effort guidance: start at `high` (the API default) and
  sweep down, rather than starting at `xhigh` for coding work.
- Add a time-to-first-token section with the prompt instruction that
  reduces pre-answer thinking on latency-sensitive routes.
- Replace the two separate thinking-disabled mitigations with the single
  combined instruction that covers both failure modes.

skills/claude-api/curl/examples.md

@@ -18,7 +18,7 @@ curl https://api.anthropic.com/v1/messages \
   -H "x-api-key: $ANTHROPIC_API_KEY" \
   -H "anthropic-version: 2023-06-01" \
   -d '{
-    "model": "claude-opus-4-8",
+    "model": "claude-opus-5",
     "max_tokens": 16000,
     "messages": [
       {"role": "user", "content": "What is the capital of France?"}
@@ -38,7 +38,7 @@ response=$(curl -s https://api.anthropic.com/v1/messages \
   -H "Content-Type: application/json" \
   -H "x-api-key: $ANTHROPIC_API_KEY" \
   -H "anthropic-version: 2023-06-01" \
-  -d '{"model":"claude-opus-4-8","max_tokens":16000,"messages":[{"role":"user","content":"Hello"}]}')
+  -d '{"model":"claude-opus-5","max_tokens":16000,"messages":[{"role":"user","content":"Hello"}]}')
 
 # Print the first text block (-r strips the JSON quotes)
 echo "$response" | jq -r '.content[0].text'
@@ -65,7 +65,7 @@ curl https://api.anthropic.com/v1/messages \
   -H "x-api-key: $ANTHROPIC_API_KEY" \
   -H "anthropic-version: 2023-06-01" \
   -d '{
-    "model": "claude-opus-4-8",
+    "model": "claude-opus-5",
     "max_tokens": 64000,
     "stream": true,
     "messages": [{"role": "user", "content": "Write a haiku"}]
@@ -104,7 +104,7 @@ curl https://api.anthropic.com/v1/messages \
   -H "x-api-key: $ANTHROPIC_API_KEY" \
   -H "anthropic-version: 2023-06-01" \
   -d '{
-    "model": "claude-opus-4-8",
+    "model": "claude-opus-5",
     "max_tokens": 16000,
     "tools": [{
       "name": "get_weather",
@@ -129,7 +129,7 @@ curl https://api.anthropic.com/v1/messages \
   -H "x-api-key: $ANTHROPIC_API_KEY" \
   -H "anthropic-version: 2023-06-01" \
   -d '{
-    "model": "claude-opus-4-8",
+    "model": "claude-opus-5",
     "max_tokens": 16000,
     "tools": [{
       "name": "get_weather",
@@ -167,7 +167,7 @@ curl https://api.anthropic.com/v1/messages \
   -H "x-api-key: $ANTHROPIC_API_KEY" \
   -H "anthropic-version: 2023-06-01" \
   -d '{
-    "model": "claude-opus-4-8",
+    "model": "claude-opus-5",
     "max_tokens": 16000,
     "system": [
       {"type": "text", "text": "<large shared prompt...>", "cache_control": {"type": "ephemeral"}}
@@ -182,17 +182,18 @@ For 1-hour TTL: `"cache_control": {"type": "ephemeral", "ttl": "1h"}`. Top-level
 
 ## Extended Thinking
 
-> **Fable 5, Opus 4.8, Opus 4.7, Opus 4.6, and Sonnet 4.6:** Use adaptive thinking. `budget_tokens` is removed on Fable 5, Opus 4.8, and 4.7 (400 if sent); deprecated on Opus 4.6 and Sonnet 4.6.
+> **Fable 5, Claude Opus 5, Opus 4.8, Opus 4.7, Opus 4.6, and Sonnet 4.6:** Use adaptive thinking. `budget_tokens` is removed on Fable 5, Claude Opus 5, Opus 4.8, and 4.7 (400 if sent); deprecated on Opus 4.6 and Sonnet 4.6.
+> **Claude Opus 5:** thinking is on by default — omitting `"thinking"` runs adaptive (`{"type": "adaptive"}` is equivalent), unlike Opus 4.8/4.7 where omitting it meant no thinking. `{"type": "disabled"}` is accepted only at effort `high` or lower; pairing it with `xhigh`/`max` returns a 400.
 > **Older models:** Use `"type": "enabled"` with `"budget_tokens": N` (must be < `max_tokens`, min 1024).
 
 ```bash
-# Fable 5 / Opus 4.8 / 4.7 / 4.6: adaptive thinking (recommended)
+# Fable 5 / Claude Opus 5 / Opus 4.8 / 4.7 / 4.6: adaptive thinking (recommended)
 curl https://api.anthropic.com/v1/messages \
   -H "Content-Type: application/json" \
   -H "x-api-key: $ANTHROPIC_API_KEY" \
   -H "anthropic-version: 2023-06-01" \
   -d '{
-    "model": "claude-opus-4-8",
+    "model": "claude-opus-5",
     "max_tokens": 16000,
     "thinking": {
       "type": "adaptive",
@@ -241,7 +242,7 @@ if [ "$(echo "$response" | jq -r '.stop_reason')" != "refusal" ] && \
 fi
 ```
 
-The header must be exactly `server-side-fallback-2026-06-01`. The parameter is rejected on the Batches API and unavailable on Amazon Bedrock, Vertex AI, and Microsoft Foundry. Full semantics (sticky routing, billing, streaming, echoing fallback turns back): `shared/model-migration.md` → Migrating to Claude Fable 5 → `refusal` stop reason.
+The header must be exactly `server-side-fallback-2026-06-01` **for this array form**; the newer `fallbacks: "default"` scalar form uses `server-side-fallback-2026-07-01` instead (see `shared/model-migration.md` → Migrating to Claude Opus 5 → New API features), and pairing either header with the other form returns a 400. The parameter is rejected on the Batches API and unavailable on Amazon Bedrock, Vertex AI, and Microsoft Foundry. Full semantics (sticky routing, billing, streaming, echoing fallback turns back): `shared/model-migration.md` → Migrating to Claude Fable 5 → `refusal` stop reason.
 
 ---