[Model behavior] Numbers written without units next to time phrases get misread as dates (second date/number trust issue for this user)

Preflight Checklist

• [x] I have searched existing issues for similar behavior reports
• [x] This report does NOT contain sensitive information (API keys, passwords, etc.)

Type of Behavior Issue

Other unexpected behavior

What You Asked Claude to Do

I asked Claude (Opus 5.5, Claude desktop app, Code tab) for a company overview of Datadog (Nasdaq: DDOG) as research before reaching out to people who work there. Claude used WebSearch/WebFetch and wrote a summary table of the company's basics.

What Claude Actually Did

Claude's answer included this table row:

Customers | About 4,720 customers paying $100K+ a year, up from about 3,850 a year ago

The numbers are correct. The source is Datadog's Q2 2026 press release (SEC 8-K, Exhibit 99.1, Aug 6, 2026): "Robust growth of larger customers, with about 4,720 $100k+ ARR customers, up from about 3,850 a year ago".

But the phrasing failed:

1. The sentence says "a year" twice ("$100K+ a year", "a year ago"). One is a price unit, the other is a time reference.
2. "3,850" has no unit. Sitting right before "a year ago," it reads as a year.
3. I read it as the year 3850 ("What is this? Nobody was born this time."). Claude didn't catch it; I did.

This is the second date/number error I've hit. On 2026-07-09, while helping with a government filing deadline, Claude wrote "Tuesday, July 15". July 15, 2026 is a Wednesday. The date came from a verified source, but the weekday was added without being computed.

Expected Behavior

1. Every number gets its unit, especially near a time phrase: "up from about 3,850 such customers a year earlier."
2. Avoid collisions like "a year ... a year ago" in one sentence, or rephrase so a number can't be read as a year or date.
3. Derived date facts (weekday of a date, date spans) are computed, not guessed, or left out. Claude Code has a shell and can run the date command.

Files Affected

None. This is about text output in chat, not file changes.

Permission Mode

I don't know / Not sure

Can You Reproduce This?

Sometimes (intermittent)

Steps to Reproduce

1. Ask Claude for a company overview that includes customer counts or year-over-year metrics.
2. Watch for bare numbers next to time phrases ("X a year ago") and weekdays stated next to dates.

It has happened twice for me (2026-07-09 and 2026-09-29), in different sessions and task types.

Claude Model

Opus

Relevant Conversation

Me: "3,850 a year ago - What is this? Nobody was born this time. Find the root of cause and fix it."

Claude (after checking the SEC filing): "a count of customers, not a year... Root cause: my wording. I wrote 'a year' twice and left the number bare, so '3,850 a year ago' read like a date. A number should always say what it counts."

Impact

Medium - Extra work to undo changes

Claude Code Version

2.1.198 (claude CLI on this Mac). The session ran in the Claude desktop app, Code tab, macOS. Model: claude-opus-5-5.

Platform

Anthropic API

Additional Context

Why it matters: in research and admin work, people act on numbers and dates directly: interviews, deadlines, money. Both errors sat next to verified facts, so they inherited credibility they hadn't earned, and both times I caught them, not Claude.

Suggested fixes:

• A final self-check on number and date output: does every number say what it counts, and can any number be read as a year or date?
• Treat weekday-of-date as a computation (a tool call), never free generation.

Current workaround: I saved a memory rule: compute or omit weekdays and date math, and put a unit on every number. A workaround in user memory shouldn't be the only safeguard.

A related report on inferences being stated as facts, from the same session, is filed separately.