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Lance Martin
b29e7cf65e
* 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.
1.6 KiB
1.6 KiB
Token Counting
Use the count_tokens endpoint (POST /v1/messages/count_tokens) for accurate
token counts against Claude models. Token counts are model-specific — pass
the same model ID you'll use for inference.
Do not use tiktoken. It's OpenAI's tokenizer. It undercounts Claude
tokens by ~15–20% on typical text, and by much more on code or non-English
input. Any estimate from tiktoken, gpt-tokenizer, or similar is wrong for
Claude.
Count a file or string
from anthropic import Anthropic
client = Anthropic()
resp = client.messages.count_tokens(
model="claude-opus-5",
messages=[{"role": "user", "content": open("CLAUDE.md").read()}],
)
print(resp.input_tokens)
TypeScript: await client.messages.countTokens({model, messages}) →
.input_tokens. See {lang}/claude-api/README.md for other SDKs.
CLI
ant messages count-tokens --model claude-opus-5 \
--message '{role: user, content: "@./CLAUDE.md"}' \
--transform input_tokens -r
Diffing a file across two versions
The endpoint is stateless — count each version separately and subtract:
from anthropic import Anthropic
import subprocess
client = Anthropic()
def count(text: str) -> int:
return client.messages.count_tokens(
model="claude-opus-5",
messages=[{"role": "user", "content": text}],
).input_tokens
before = subprocess.check_output(["git", "show", "HEAD:CLAUDE.md"], text=True)
after = open("CLAUDE.md").read()
print(count(after) - count(before))
Full docs: see the Token Counting entry in shared/live-sources.md.