Examples of situations where gemini-flash ignores the provided prefill. Switching to pro works fine however.

flash-prefill.txt

curl https://generativelanguage.googleapis.com/v1beta/models/gemini-1.5-flash-latest:generateContent?key=$GOOGLE_API_KEY     -H 'Content-Type: application/json'     -X POST     -d '{ "contents":[ {"role": "user", "parts":[{"text": "Write a story about a magic backpack."}] }, {"role": "model", "parts":[{"text": "There was never"}] } ] }'
curl https://generativelanguage.googleapis.com/v1beta/models/gemini-1.5-flash-latest:generateContent?key=$GOOGLE_API_KEY     -H 'Content-Type: application/json'     -X POST     -d '{ "contents":[ {"role": "user", "parts":[{"text": "What is your favorite color?"}] }, {"role": "model", "parts":[{"text": "Orange is"}] } ] }'
curl https://generativelanguage.googleapis.com/v1beta/models/gemini-1.5-flash-latest:generateContent?key=$GOOGLE_API_KEY     -H 'Content-Type: application/json'     -X POST     -d '{ "contents":[ {"role": "user", "parts":[{"text": "List 4 colors."}] }, {"role": "model", "parts":[{"text": "- "}] } ] }'
curl https://generativelanguage.googleapis.com/v1beta/models/gemini-1.5-flash-latest:generateContent?key=$GOOGLE_API_KEY     -H 'Content-Type: application/json'     -X POST     -d '{ "contents":[ {"role": "user", "parts":[{"text": "Make a step by step plan of how to calculate whether a number is a prime using Python."}] }, {"role": "model", "parts":[{"text": "1. "}] } ] }'
curl https://generativelanguage.googleapis.com/v1beta/models/gemini-1.5-flash-latest:generateContent?key=$GOOGLE_API_KEY     -H 'Content-Type: application/json'     -X POST     -d '{ "contents":[ {"role": "system", "parts":[{"text": "You always respond with steps as a numbered list, never with code."}] }, {"role": "user", "parts":[{"text": "How do you calculate where a number is prime?"}] }, {"role": "model", "parts":[{"text": "1. "}] } ] }'