@3bf0c63fcb93463407af97a5e5ee64fa883d107ef9e558472c4eb9aaaefa459d They made it intentionally not incompatible:

["REQ", "amelx49c18", {"cache": ["net_stats"]}]
["CLOSE", "amelx49c18"]

["REQ", "p0xren2axa", {"cache": ["feed", {"pubkey": "64-hex digits of pubkey id"}]}]

["REQ", "vqvv4vc6us", {"cache": ["thread_view", {"event_id": "64-hex digits of event id"}]}]

["REQ", "ay4if6pykg", {"cache": ["user_infos", {"pubkeys": ["64-hex digits of pubkey id"]}]}]

["REQ", "2t6z17orjp", {"cache": ["events", {"event_ids": ["64-hex digits of event id"]}]}]

["REQ", "1uddc0a2fv", {"cache": ["user_profile", {"pubkey": "64-hex digits of pubkey id"}]}]

Filter is extended to have an extra "cache" key. But I don't think they serve normal filters from this.