Public reporting shows that Russia did not fully “mop up” or expel the Ukrainian incursion force from Russia’s Kursk region within roughly a year, and that Ukraine still maintains a (small) foothold there even now.

Key points:

• Ukraine launched its Kursk offensive on 6 August 2024, seizing over 1,000–1,300 km² of Russian territory and dozens of settlements, including the town of Sudzha. (en.wikipedia.org)
• By November 2024, Ukraine had lost more than 40% of the territory it had initially seized, and by 12 March 2025 Russia had retaken Sudzha and much of the Ukrainian-held area, significantly shrinking the bridgehead. (en.wikipedia.org)
• Reuters in March 2025 reported Russia was nearing complete expulsion of Ukrainian troops and that Ukraine’s foothold had dwindled to <81 km², but even then it was not entirely eliminated. (reuters.com)
• On 22 June 2025 (about ten months after the incursion started and within the “roughly a year” window), Ukraine’s commander-in-chief Oleksandr Syrskyi told the BBC that Ukrainian forces were still holding about 90 km² of territory in the Kursk region despite about 10,000 Russian troops trying to dislodge them. (feeds.bbci.co.uk)
• On 6 August 2025, at the one‑year anniversary of the operation, Ukrainian command again stated that their forces continued to hold positions in the Glushkivskyi district of Russia’s Kursk region. (mezha.net)
• Subsequent reporting and analysis (ISW‑summarized in the Kursk campaign article, and Ukrainian/Ukrinform statements) confirms that as of late 2025 Ukraine still maintains some positions on Russian territory in the Kursk sector. (en.wikipedia.org)

It is true that Ukraine has suffered heavy losses and has been pushed back from most of the territory it initially seized; several analysts describe the Kursk operation as costly and, in strategic terms, at least a partial failure. (en.wikipedia.org) But Sacks’s specific prediction was that Russia would essentially wipe out the Kursk bridgehead over time—“mop them up”—rather than allow a durable foothold.

Given that Ukrainian forces still hold a small but persistent pocket of territory inside Russia more than a year after the offensive began, the core of that prediction (complete defeat/forced withdrawal within roughly a year, no lasting foothold in Russia) has not come true.

Therefore, the prediction is best judged as wrong.