| Tengen published the NES cartridge without Nintendo's license. Its manual prints "KLAX: TM Atari Games; licensed to Tengen, Inc. ©1990 Tengen, Inc" and refers players to Tengen's game counselors; Tengen's advertisement in Electronic Gaming Monthly's August 1990 issue says Tengen's products are not designed, manufactured, sponsored or endorsed by Nintendo, and that Klax was "Appearing first on the NES", to follow on the Genesis, the TurboGrafx and home computers. Nintendo of America's list of NES games has no entry for Klax. | image 3, Tengen advertisementimage 3, Tengen advertisementimage 3, Tengen advertisement | Manual |
| The NES version was out by the summer of 1990: Electronic Gaming Monthly's Review Crew reviewed it in the August 1990 issue, whose review header gives its release as July, and Tengen advertised it in the same issue. Chris Scullion's NES Encyclopedia (2019) gives 1990, and Tengen as publisher and developer. No source read gives a day of release. | image 14, Review Crewimage 3, Tengen advertisementp. 14 (image 14), Review Crew, Klax header, read on the page image | Magazine |
| Electronic Gaming Monthly's Review Crew reviewed the NES version in its August 1990 issue: Steve gave it 7, Ed 6, Martin 7 and Sushi-X 7, out of 10. The header lists a Tengen puzzle game with 50 levels, and the description calls it an adaptation of "the recent Atari Games coin-op hit", a puzzle game "somewhat resembling a cross between Tetris and Columns". Steve called it "Tengen's revenge against Nintendo", with graphics and sound "remarkably close to the arcade, but more diversity in play would be nice". Ed found it different enough from Tetris to have its own identity. Martin called it "A good arcade translation of Klax for NES" that loses its appeal after 20 rounds, but "A good game!". Sushi-X called it "one great game idea which has gone astray", without "the 'progressive' appeal that you get with Tetris." | image 14, Review Crew, Klaximage 14, Review Crew, Klaximage 14, Review Crew, Klaximage 14, Review Crew, Klaximage 14, Review Crew, Klaximage 14, Review Crew, Klaximage 14, Review Crew, Klaximage 14, Review Crew, Klaxp. 14 (image 14), Review Crew, Klax, read on the page imagep. 14 (image 14), Review Crew, Klax, read on the page imagep. 14 (image 14), Review Crew, Klaxp. 14 (image 14), Review Crew, Klax, read on the page imagep. 14 (image 14), Review Crew, Klax, read on the page image | Magazine |
| By 1991 Klax had appeared on many systems. Atari's Lynx advertising in Electronic Gaming Monthly's August 1990 issue offered Klax, "The latest arcade mega-hit from Atari Games", with 100 levels; Game Player's capsule of June 1991 lists Tengen's Klax for the NES, NEC, Genesis, Lynx, PC, Amiga, ST and 64. In May 1991 Nintendo Power listed Klax among the Game Boy games coming from Mindscape. | image 53, Atari Lynx advertisementimage 53, Atari Lynx advertisement | Magazine |
| Electronic Gaming Monthly described the NES game in August 1990, counting six levels, and called it Ocean's "first Nintendo cartridge". | p. 44 (image 46), Untouchablesp. 44 (image 46), Untouchablesp. 44 (image 46), Untouchables | Magazine |