context-budget

Context Budget — Token Estimation

Estimate how many tokens a file or directory will consume before reading it.

How to Estimate

Rule of thumb: 1 token ≈ 4 characters (English text/code). This is a rough estimate.

Opus 4.7 tokenizer note: Opus 4.7 uses a new tokenizer that can produce up to 35% more tokens for the same text vs. prior models. If the user is on Opus 4.7, multiply the rough estimate by ~1.35 for a conservative upper bound. Opus 4.6, Sonnet 4.6, and Haiku 4.5 use the older tokenizer.

When the user asks about a file or directory:

1. Get the file size in bytes using:

wc -c < "filepath"

Or for a directory:

find "dirpath" -type f -exec wc -c {} + | tail -1

1. Estimate tokens: file_size_bytes / 4 (add ~35% headroom if they're on Opus 4.7)

2. Show the estimate with context AND model comparison:

File: path/to/file.py
Size: 12,400 bytes
Est. tokens: ~3,100 (~4,200 on Opus 4.7)
Context impact: 0.3% of 1M window

Cost to read (first time / cached):
  Opus 4.7: $0.016 / $0.002
  Opus 4.6: $0.016 / $0.002
  Sonnet 4.6: $0.009 / $0.001
  Haiku 4.5: $0.003 / $0.0003

Use these prices per 1M tokens for the comparison:

Model	Input	Cache Read	Cache Write (5m)	Output
Opus 4.7	$5.00	$0.50	$6.25	$25.00
Opus 4.6	$5.00	$0.50	$6.25	$25.00
Sonnet 4.6	$3.00	$0.30	$3.75	$15.00
Haiku 4.5	$1.00	$0.10	$1.25	$5.00

Opus 4.7 and 4.6 share the same per-token pricing. The 1M-context variants (claude-opus-4-7[1m], claude-opus-4-6[1m], claude-sonnet-4-6[1m]) are also at standard pricing — no long-context premium.

• "First time" = input price (first read, not yet cached)
• "Cached" = cache read price (subsequent reads in same session)
• Always show all four models so users can compare

For directories, also show file count and breakdown of largest files.

Context Impact Table

Tokens	% of 1M	% of 200K	Verdict
< 1K	0.1%	0.5%	Trivial
1-5K	0.1-0.5%	0.5-2.5%	Light
5-20K	0.5-2%	2.5-10%	Moderate
20-50K	2-5%	10-25%	Heavy — consider reading specific sections
50K+	5%+	25%+	Very heavy — read only what you need