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Transform Casual Sentences into Formal Writing

Tested prompts for rewrite sentence in formal tone compared across 5 leading AI models.

BEST BY JUDGE SCORE Claude Haiku 4.5 8/10

The prompt we tested

You are an expert editor specializing in formal writing. Rewrite the following sentence(s) in a formal tone while preserving the original meaning.

Rules to follow:
Replace contractions, slang, and casual phrasing with professional vocabulary; use complete, grammatically precise sentences; maintain a neutral, objective tone without changing the original meaning or adding new information. Keep the rewrite roughly the same length as the original.

Original text:
Hey, just wanted to let you know we can't make it to the meeting tomorrow because something came up. Can we reschedule for next week? Thanks a bunch!

Provide only the rewritten formal version, with no explanations or commentary.

Model comparison

ModelQualityCostLatencyTokens
Claude Opus 4.7 7 $0.0101 2.7s 231 / 88
Claude Haiku 4.5 8 $0.0004 2.1s 153 / 51
GPT-5.4 8 $0.0008 3.1s 133 / 34
Gemini 2.5 Pro 8 $0.0003 16.7s 133 / 28
Grok 4.1 Fast Reasoning 8 $0.0001 7.9s 282 / 35

Outputs

Claude Opus 4.7 7/10 
Dear Sir or Madam,

I am writing to inform you that we will be unable to attend tomorrow's meeting, as an unforeseen matter has arisen. Would it be possible to reschedule the meeting for next week? Thank you very much for your understanding.
Judge notes: The addition of "Dear Sir or Madam" and "for your understanding" introduces content not present in the original, violating the instruction not to add new information, and the salutation was not requested.
Claude Haiku 4.5 8/10 
We regret to inform you that we are unable to attend the scheduled meeting tomorrow due to an unforeseen circumstance. We respectfully request that the meeting be rescheduled for the following week. Thank you for your understanding.
Judge notes: "Thank you for your understanding" adds a phrase not present in the original ("Thanks a bunch" implies gratitude but not specifically for understanding), which slightly violates the rule against adding new information.
GPT-5.4 8/10 
I wanted to inform you that we are unable to attend the meeting tomorrow due to an unforeseen circumstance. Could we reschedule for next week? Thank you.
Judge notes: The rewrite is clean and professional, but "unforeseen circumstance" slightly embellishes the original ("something came up"), and the opening drops the greeting without replacing it with an appropriate formal salutation, making it feel slightly abrupt.
Gemini 2.5 Pro 8/10 
Due to a scheduling conflict, we are unable to attend the meeting tomorrow. Would it be possible to reschedule for next week? Thank you.
Judge notes: The rewrite is clean and accurate, but "a scheduling conflict" adds slight specificity not in the original ("something came up" is intentionally vague), which marginally violates the no-new-information rule.
Grok 4.1 Fast Reasoning 8/10 
I am writing to inform you that we cannot attend the meeting tomorrow, as an unforeseen matter has arisen. Would it be possible to reschedule for next week? Thank you.
Judge notes: "An unforeseen matter has arisen" slightly over-formalizes "something came up" by adding an implicit characterization (unforeseen) not present in the original, which violates the rule against adding new information.

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